In 1978 the Secretary of Labor promulgated "interim regulations" to govern the processing of claims for black lung benefits filed between July 1, 1973, and April 1, 1980. See 20 CFR pt. 727 (1987). Section 203 of those regulations prescribes five ways in which a claimant may prove that he is entitled to an "interim presumption" of eligibility. The question in this case concerns the burden of proof that the claimant must satisfy to invoke the presumption. The Court of Appeals held, Stapleton v. Westmoreland Coal Co., 785 F.2d 424 (CA4 1986) (en banc) (case below), that a single item of qualifying evidence is always sufficient whereas the Secretary of Labor contends that his regulation requires the claimant to establish at least one of the five qualifying facts by a preponderance of the evidence. Because we are not persuaded that the Secretary has misread his own regulation, we reverse.

* Although some aspects of the black lung benefits program are rather complex, its broad outlines and relevant statutory provisions can be briefly described. Prolonged exposure to coal dust has subjected hundreds of thousands of coal miners to pneumoconiosis—a serious and progressive pulmonary condition popularly known as "black lung." The tragic consequences of this crippling illness prompted Congress to authorize a special program for the benefit of its victims in 1969. Because that program has been developed through several statutory enactments,1 different rules govern claims filed during different periods of time. Those filed prior to July 1, 1973, were processed by the Social Security Administration (SSA) pursuant to regulations promulgated by the Secretary of the Department of Health, Education, and Welfare (HEW); when allowed, these "Part B" claims were paid from federal funds.2 "Part C" claims3 are those filed on or after July 1, 1973; they are paid by private employers or by a fund to which the employers contribute, and they are administered by the Director of the Office of Workers' Compensation Programs (the Director) pursuant to regulations promulgated by the Secretary of Labor (the Secretary). Part C of the program includes two subparts: claims filed after April 1, 1980, which are governed by "permanent criteria,"4 and those filed prior to April 1, 1980, which are governed by the "interim regulations" at issue in this case. Despite the "interim" designation, these regulations are extremely important because they apply to about 10,000 pending claims.

There is no dispute about the Secretary's authority to promulgate the interim regulations.5 Nor is there any suggestion that they violate any express statutory command. The statute does require the Secretary to establish criteria for eligibility that "shall not be more restrictive than" the criteria that the Secretary of HEW had established for the administration of the Part B program,6 but the Court of Appeals did not hold that § 203 violates this standard. The statute also requires that "all relevant evidence" shall be considered, but it is clear that the regulation is consistent with that requirement7—the only dispute is over how much of the relevant evidence may be considered in determining whether the interim presumption shall be invoked. Thus, there is no need to parse statutory language to decide this case.

The Court of Appeals' holding rests, at bottom, on two propositions: (1) the regulation's plain language mandates that the presumption be invoked on the basis of a single item of qualifying evidence; and (2) the Secretary's reading is not faithful to the purposes of the program as reflected in its legislative history. We shall consider each of these propositions after reviewing the substance of the regulation and the facts of the one case that presents the legal question we must decide.8

Disability benefits are payable to a miner if (a) he or she is totally disabled, (b) the disability was caused, at least in part, by pneumoconiosis, and (c) the disability arose out of coal mine employment. All three of these conditions of eligibility are presumed if the claimant was engaged in coal mine employment for at least ten years and if the claimant meets one of four medical requirements:9 (1) a chest X-ray establishes the presence of pneumoconiosis; (2) ventilatory studies establish the presence of a respiratory or pulmonary disease—not necessarily pneumoconiosis of a specified severity; (3) blood gas studies demonstrate the presence of an impairment in the transfer of oxygen from the lungs to the blood; or (4) other medical evidence, including the documented opinion of a physician exercising reasonable medical judgment, establishes the presence of a totally disabling respiratory impairment.10 It is noteworthy that only the first of the four alternative methods of invoking the presumption requires proof that the claimant's disease is in fact pneumoconiosis. None of the methods requires proof of causation, and only the fourth requires proof of total disability.

The second paragraph in the regulation describes how the presumption may be rebutted.11 It first provides that in the adjudication of a claim, "all relevant medical evidence shall be considered." It then provides that the presumption is rebutted if the evidence establishes that the claimant is doing or is capable of doing his usual or comparable work, that his disability did not arise, even in part, out of coal mine employment, or that he does not have pneumoconiosis. Thus, in order to rebut the interim presumption the employer has the burden of proving that at least one of the three conditions of eligibility is not satisfied.12

Respondent Ray filed a claim for disability benefits with the Secretary in 1976. At the hearing before the ALJ, he proved that he had 16 years of coal mine employment. The ALJ placed 47 exhibits from the Director's file into evidence,13 and the employer introduced four additional exhibits. The record contained one qualifying14 X-ray interpretation, two qualifying ventilatory studies, and one qualifying physician's opinion. The record, however, also included seven nonqualifying X-ray interpretations, four nonqualifying ventilatory studies, and five nonqualifying physicians' opinions.15 After weighing the X-ray evidence, the ALJ concluded that it did not establish that Ray had pneumoconiosis,16 and afterbalancing all the ventilatory studies, he concluded that they did not establish the presence of a chronic respiratory or pulmonary disease.17 Additionally, the ALJ found that the other medical evidence, including documented physicians' opinions, did not establish the presence of a totally disabling respiratory or pulmonary impairment.18 He therefore held that Ray was not entitled to the benefit of the interim presumption.19

The BRB affirmed the ALJ's order denying benefits. It first noted that Ray's "contention that subsection (a)(1) must be invoked where the record contains a single positive X-ray has previously been considered and rejected,"20 and it agreed with the ALJ's evaluation of the X-ray evidence and ventilatory studies. Finally, while disagreeing with some of the ALJ's reasoning, the Board reviewed and approved the ALJ's weighing of the physicians' opinions in the employer's favor.

The Court of Appeals remanded for further proceedings. It held that the interim presumption had been invoked under § (a)(2) by the two qualifying ventilatory studies and under § (a)(4) by the one qualifying physician's opinion. The court did not rely on the positive X-ray interpretation because it was not sufficiently identified to satisfy the requirements for X-ray evidence under § 718.102(c) of the Secretary's regulation. The court reversed the Board's denial of benefits and remanded for the ALJ to determine whether the presumption had been rebutted. We granted certiorari, 479 U.S. ----, 107 S.Ct. 871, 93 L.Ed. 826 (1987), to resolve the question presented by this case: whether one item of qualifying evidence is always sufficient to invoke the interim presumption and thereby shift the burden of persuasion to the employer.

The Court of Appeals held that "the interim presumption under § 727.203(a)(1), (2), or (3) is established when there is credible evidence that a qualifying X-ray indicates the presence of pneumoconiosis, a single qualifying set of ventilatory studies indicates, pursuant to the regulatory standard, a chronic respiratory or pulmonary disease, or a single qualifying set of blood gas studies indicates, pursuant to the regulatory standard, an impairment in the transfer of oxygen from the lungs to the blood." 785 F.2d, at 426. The principal basis for this holding was the court's view that the plain language of the regulation makes it clear that a single positive X-ray necessarily invokes the presumption. In advancing that view, however, the court did not pause to consider the significance ofthe word "establishes" in § (a)(1). It read § (a)(1) as though it merely required a chest X-ray that constitutes evidence of the presence of pneumoconiosis rather than one that actually "establishes" the presence of the disease.

The Secretary's regulations, however, recognize the difference between an X-ray that tends to prove the presence of pneumoconiosis and one that can be said to establish it. Thus, in contrast to the use of the word "establishes" throughout § 727.203(a), the regulation defining the suitable quality of X-ray evidence refers to an X-ray that "shall constitute evidence of the presence or absence of pneumoconiosis."21 The Court of Appeals read § 203(a)(1) as though it merely required an X-ray that "constitutes evidence of the presence of pneumoconiosis." Had that been the Secretary's intent, presumably he would have used that language as he did elsewhere to explain that meaning.

There is another reason why § (a)(1) cannot have been intended to refer to a single item of evidence. For the ordinary trier of fact—even an ALJ who has heard many black lung benefit cases—an X-ray may well be meaningless unless it is interpreted by a qualified expert. What may be persuasive to the ALJ, then, is not just the X-ray itself, but its interpretation by a specialist. And, of course, different experts may provide different readings of the same X-ray. As Judge Posner has observed:

"Under the regulation it is not the reading, but the X-ray, that establishes the presumption. If one doctor interprets an X-ray as positive for black-lung disease but 100 equally qualified doctors interpret the same X-ray as negative for the disease, nothing in the regulation requires the administrative law judge to disregard the negative readings." Cook v. Director, Office of Workers' Compensation Programs, 816 F.2d 1182, 1185 (CA7 1987).

Thus, it seems perfectly clear that it is not the X-ray in isolation that "establishes" the presence of the disease; rather, the regulation must, at a minimum, have reference both to the X-ray itself and to other evidence that sheds light on the meaning and significance of the X-ray.22 Just as the ALJ must weigh conflicting interpretations of the same X-ray in order to determine whether it tends to prove or disprove the existence of pneumoconiosis, there would seem to be no reason why he must ignore all X-rays in a series except one.23

The Court of Appeals relied in large part on perceived internal inconsistencies in the Secretary's interpretation. In the rebuttal section, the regulation provides that in "adjudicating a claim under this subpart, all relevant medical evidence shall be considered." The Court of Appeals interpreted this statement as requiring all relevant evidence to be considered on rebuttal. Since the Secretary's reading would make some evidence inadmissible for certain aspects of rebuttal,24 the Court of Appeals thought that reading violated the requirement that "all relevant medical evidence shall be considered."

We disagree, for two reasons. First, nothing in the Secretary's position prevents "all relevant medical evidence" from being considered at some point during the proof process. To understand why this requirement was inserted at the beginning of the rebuttal section, it is important to understand its derivation. After the SSA adopted its interim presumption, its claims approval rate increased, in part due, it is thought, to factfinders failing to consider all of the employers' relevant medical evidence.25 To assure that this problem would not infect adjudications under the new Labor interim presumption, the requirement of 30 U.S.C. § 923(b) that all relevant medical evidence be considered in adjudicating SSA claims was explicitly carried over into the Labor presumption's rebuttal section. Thus, that the "all relevant medical evidence" requirement appears at the beginning of the rebuttal section reflects the genesis of the concern and does not indicate that the drafters intended a more limited evidentiary battle at the invocation stage. As long as relevant evidence will be considered at some point by the ALJ, the demand that the decision be made on the complete record is satisfied.

Second, the cited provision refers to "adjudicating a claim under this subpart," and a "subpart" "may be used to group related sections in a part." 1 CFR § 21.9(b) (1987). All of 20 CFR § 727.203 (1987), the interim presumption, is within subpart C of part 727. Thus, nothing in the regulation requires all relevant medical evidence to be considered at the rebuttal phase; such evidence must simply be admissible at some point during the proof process.

The Court of Appeals was persuaded as well that some of the rebuttal provisions would be superfluous under the Secretary's reading. For instance, if the claimant invokes the presumption by establishing the existence of pneumoconiosis under § (a)(1), the employer may not try to disprove pneumoconiosis under § (b)(4). This limitation on rebuttal, according to the Court of Appeals, renders the Secretary's position internally inconsistent.

Again, we are constrained to disagree. Nothing in the regulation requires each rebuttal subsection to be fully available in each case. As long as the employer can introduce, say, nonqualifying X-rays at the invocation stage to oppose invocation under § (a)(1), it has been given the chance to show the nonexistence of pneumoconiosis. If the presumption is nonetheless invoked, the employer can still try to disprove total disability or causality.26

Finally, there is some concern that the Secretary's position might permit a single negative X-ray interpretation to carry the day for the employer, in violation of the statute's mandate that "no claim for benefits . . . shall be denied solely on the basis of the results of [an X-ray]." § 923(b) (made applicable to Part C adjudications through § 902(f)(2)). The easy answer was provided by the dissent below: "a single negative X-ray may not . . . be drawn upon either as the sole basis for finding the invocation burden under (a)(1) not carried nor as the sole basis for finding the rebuttal burden under (b)(4) carried." 785 F.2d, at 445 (emphases added). Furthermore, in weighing conflicting X-ray readings ALJs will undoubtedly keep in mind the character of the black lung disease:

"Since pneumoconiosis is a progressive and irreversible disease, early negative X-ray readings are not inconsistent with significantly later positive readings. . . . This proposition is not applicable where the factual pattern is reversed. In a situation . . . where the more recent X-ray evidence is negative and directly conflicting with earlier positive X-rays it may be weighed with less regard to timing in light of the recognized principle that negative X-ray readings are not a trustworthy indicator of the absence of the disease." Elkins v. Beth-Elkhorn Corp., 2 BLR 1-683, 1-686 (Ben.Rev.Bd.1979).

In sum, we find the Secretary's interpretation of his own regulation entirely consistent with its text.

The Court of Appeals' holding that a single item of qualifying evidence always suffices to carry a claimant's invocation burden was based in part on its understanding of the legislative history of the black lung benefits statutes. 785 F.2d, at 457-461. This conclusion is based on the clear congressional mandate for interim presumptions to reduce the number of benefit denials by both the SSA and Labor. While we agree that Congress did intend to ensure fewer benefit denials, we are not persuaded either that that goal has been frustrated by the Secretary's interpretation of the regulation, or that Congress intended more specifically to require invocation of the presumption based solely on one item of a claimant's proof.

In the early years of the benefits program, the SSA denied a high number of claims because of a perceived lack of proof of totally disabling pneumoconiosis due to coal mine employment. Congress mandated liberalized standards, and the SSA established an interim presumption to carry out this directive. § 410.490(b). In so doing, the SSA explained the problems with the prior scheme and the virtues of the new one:

"In enacting the Black Lung Act of 1972, the Congress noted that adjudication of the large backlog of claims generated by the earlier law could not await the establishment of facilities and development of medical tests not presently available to evaluate disability due to pneumoconiosis, and that such claims must be handled under present circumstances in the light of limited medical resources and techniques. Accordingly, the Congress stated its expectancy that the Secretary would adopt such interim evidentiary rules and disability evaluation criteria as would permit prompt and vigorous processing of the large backlog of claims consistent with the language and intent of the 1972 amendments and that such rules and criteria would give full consideration to the combined employment handicap of disease and age and provide for the adjudication of claims on the basis of medical evidence other than physical performance tests when it is not feasible to provide such tests. The provisions of this section establish such interim evidentiary rules and criteria. They take full account of the congressional expectation that in many instances it is not feasible to require extensive pulmonary function testing to measure the total extent of an individual's breathing impairment, and that an impairment in the transfer of oxygen from the lung alveoli to cellular level can exist in an individual even though his chest roentgenogram (X-ray) or ventilatory function tests are normal." § 410.490(a).

The SSA implemented this congressional desire to ease claimants' proof burdens by promulgating the interim presumption that serves as the antecedent to the one at issue in this case. The presumption, applicable to claims filed with the SSA before July 1, 1973, provides that a miner is presumed to be totally disabled due to pneumoconiosis if two conditions are met: First, either "[a] chest . . . X-ray . . . establishes the existence of pneumoconiosis" or "[i]n the case of a miner employed for at least 15 years in underground or comparable coal mine employment, ventilatory studies establish the presence of a chronic respiratory or pulmonary disease. . . ." § 410.490(b)(1); second, "[t]he impairment established in accordance with [either of these medical requirements] arose out of coal mine employment." § 410.490(b)(2). Additionally, "a miner who meets the [ventilatory studies] medical requirements . . . will be presumed to be totally disabled due to pneumoconiosis arising out of coal mine employment . . . if he has at least 10 years of the requisite coal mine employment." § 410.490(b)(3).

The SSA's interim rules further provide that the presumption can be rebutted if either "[t]here is evidence that the individual is, in fact, doing his usual coal mine work or comparable and gainful work" or "[o]ther evidence, including physical performance tests . . ., establish[es] that the individual is able to do his usual coal mine work or comparable and gainful work." § 410.490(c).

As the SSA's claims approval rate increased, Labor's remained low, in large part because of the absence of an interim presumption by which a claimant would only have to prove one predicate fact. The interim presumption at issue in this case, promulgated as a result of congressional dissatisfaction with Labor's low claims approval rate, is substantially similar to the SSA interim presumption. It satisfies Congress' demand that Labor's criteria "shall not be more restrictive than the criteria applicable to a claim filed on June 30, 1973," 30 U.S.C. § 902(f)(2), i.e., no more restrictive than the SSA's interim presumption.

Since Labor's interim presumption derived so directly from the SSA's, if the Court of Appeals' conclusion regarding single-item invocation were correct, one would expect to find SSA ALJ decisions permitting invocation in such a manner, and federal court opinions indicating approval. Instead, federal court decisions routinely referred to SSA ALJ invocation weighings without objection, and often with explicit approval.27 Thus, the legislative history of the Labor interim presumption does not establish that invocation must occur on a single piece of qualifying evidence.28

Under either the Court of Appeals' or the Secretary's interpretation of the regulation, a single item of qualifying evidence may be sufficient to invoke the presumption. Indeed, the authors of the regulation apparently expected that the presumption would regularly be invoked on the basis of a single item of qualifying evidence.29 Reasoning from that expectation, the Court of Appeals concluded that the presumption must be invoked whenever the record contains a single item of qualifying evidence. But as we have demonstrated above, that conclusion is compelled by neither the text nor the history of the regulation.

Nor is it compelled by the underlying basis for the presumption. For black lung benefits presumptions, no less than any presumption established or recognized in law, are the product of both factual understandings and policy concerns. As a matter of fact, Congress could reasonably have concluded that it is highly probable that a person who engaged in coal mine employment for over a decade is totally disabled as a result of pneumoconiosis arising from that employment if he or she can prove any of the medical requirements specified in the regulation.30 That degree of probability is not, however, present when the claimant is merely in a position to offer a single item of qualifying evidence that is overcome by more reliable conflicting evidence.

As a matter of policy, Congress was aware that it is difficult for coal miners whose health has been impaired by the insidious effects of their work environment to prove that their diseases are totally disabling and coal-mine related, or that those diseases are in fact pneumoconiosis. Rather than merely providing a benefit for those miners who could prove each of the relevant facts by a preponderance of the evidence, Congress intended that those long-term miners who can show that they are truly diseased should have to prove no more.31 But if a miner is not actually suffering from the type of ailment with which Congress was concerned, there is no justification for presuming that that miner is entitled to benefits. For not only does that miner fall outside the class of those who need the assistance of an interim presumption, but he also is unlikely to be totally disabled from coal mine employment. By requiring miners to show that they suffer from the sort of medical impairment that initially gave rise to congressional concern, and then by requiring employers to shoulder the remainder of the proof burden, the Secretary's reading of the interim presumption's invocation burden satisfies both the purposes of the statute and the need for a logical connection between the proven fact and the presumed conclusion.32

In the end, the Secretary's view is not only eminently reasonable but also is strongly supported by the fact that Labor wrote the regulation. The Agency's interpretation, which is deserving of substantial deference "unless it is plainly erroneous or inconsistent with the regulation," Bowles v. Seminole Rock & Sand Co., 325 U.S. 410, 414, 65 S.Ct. 1215, 1217, 89 L.Ed. 1700 (1945), has been, with one exception, consistently maintained through Board decisions.33 Likewise, prior to the Court of Appeals decision in this case, the Courts of Appeals had routinely reviewed for substantial evidence the factfinder's invocation determination under a preponderance of the evidence standard.34 Accordingly, there is no reason to downgrade the normal deference accorded to an agency's interpretation of its own regulation. Cf. Motor Vehicle Mfrs. Assn. of the United States, Inc. v. State Farm Mutual Automobile Insurance Co., 463 U.S. 29, 103 S.Ct. 2856, 77 L.Ed.2d 443 (1983).

The judgment of the Court of Appeals is reversed and the case is remanded for further proceedings consistent with this opinion.35

It is so ordered.

Justice MARSHALL, with whom Justice BRENNAN joins, dissenting.

This case concerns the evidentiary threshold that a claimant of black lung benefits must meet to invoke the interim presumption of total disability due to pneumoconiosis under 20 CFR § 727.203(a) (1987). The Director of the Office of Workers' Compensation (Director) interprets the regulation to require that a claimant prove by a preponderance of the evidence one of the four medical requirements listed in § 727.203(a) to trigger the presumption. The Court of Appeals, en banc, rejected the Director's proffered interpretation and held that the presumption is invoked once the claimant has presented a single item of evidence meeting one of the medical requirements—that is, "one positive x-ray, one qualifying set of ventilatory or blood gas studies, or one physician's opinion." Stapleton v. Westmoreland Coal Co., 785 F.2d 424, 436 (CA4 1986). The Court chooses to embrace the Director's view. Because I believe that the Director's interpretation of the regulation contravenes its plain language and creates a regulatory scheme that is unnecessarily complex and internally inconsistent, I dissent.

* The language and structure of the regulation provide the most compelling evidence for rejecting the Director's interpretation. The regulation sets up two evidentiary stages: part (a), the presumption-invocation stage, and part (b), the rebuttal stage. Part (a) provides that a "miner who engaged in coal mine employment for at least 10 years will be presumed to be totally disabled due to pneumoconiosis" as long as the miner meets any one of four medical requirements. § 727.203(a). Part (b) provides that the presumption is rebutted if the Administrative Law Judge (ALJ) determines that the claimant is doing or could do his usual coal mine work or comparable gainful work; that the disability "did not arise in whole or in part out of coal mine employment"; or that the "evidence establishes that the miner does not, or did not, have pneumoconiosis." § 727.203(b).

Under § (a)(1), the presumption is triggered when "[a] chest [X ray], biopsy, or autopsy establishes the existence of pneumoconiosis." Under § (a)(4), the presumption is triggered when "[o]ther medical evidence, including the documented opinion of a physician exercising reasoned medical judgment, establishes the presence of a totally disabling respiratory or pulmonary impairment." The regulation does not refer to "the X-ray evidence taken as a whole," or "the weight of documented opinions of physicians"—the inquiry mandated by the Court's interpretation—but rather to an X ray, or a physician's opinion. Moreover, the regulation does not provide that a claimant who presents a single qualifying piece of evidence may be presumed to be totally disabled because of pneumoconiosis, but rather provides that such a claimant "will be presumed" totally disabled because of the disease. The regulation thus expressly commands that a single qualifying X ray or a single documented physician's opinion will trigger the presumption.1

The Court attempts to evade the plain meaning of the regulation by placing overriding emphasis on the regulation's use of the word "establishes." The Court interprets "establish" to mean that a claimant must prove each of the medical requirements by a preponderance of the evidence.2 Under this interpretation, an ALJ must weigh conflicting like-kind evidence before invoking the presumption. A more natural reading of "establish" in the context of the presumption-invocation stage, however, is simply that the ALJ must determine whether a claimant has come forward with an X ray, a set of ventilatory or blood gas studies, or a physician's opinion that meets the requirements and standards of the regulation. In other words, an ALJ determines whether the single item of evidence "establishes the existence of pneumoconiosis" or "establishes the presence of a totally disabling respiratory or pulmonary impairment" by referring to the strict reliability and authenticity requirements of the regulations, see, e.g., 20 CFR §§ 410.428, 727.206 (1987), and, with regard to ventilatory and blood gas studies, to the qualifying standards set out in § 727.203(a).

The Court argues that § (a)(1) cannot have been intended to refer to a single item of evidence because an X ray is probative only when it is interpreted by a qualified expert. The Court reasons that because the presumption is invoked by an X ray, and not by an expert's reading, an ALJ may have to consider different interpretations of the same X ray. From this premise, the Court concludes that "[j]ust as the ALJ must weigh conflicting interpretations of the same X-ray . . ., there would seem to be no reason why he must ignore all X-rays in a series except one." Ante, at 148—149 (footnote omitted). No reason except the regulatory language. Whatever the merit of the Court's conclusion that conflicting readings of the same X ray must be weighed prior to invoking the presumption (for that question is not before the Court), the regulation's plain language requires that the presumption be invoked when a single X ray is read only as positive. In addition, contrary to the Court's characterization, additional X rays that indicate the absence of pneumoconiosis are not "ignored"; they are fully considered by the ALJ during the rebuttal stage, when all evidence against the presumed existence of pneumoconiosis is brought to bear.3

The Court of Appeals ruling that a single qualifying test or medical opinion is sufficient to invoke the presumption is further supported by the comments that the Secretary of Labor issued in connection with the final promulgation of the regulations. In addressing the standard of rebuttal, the Secretary stated: "[T]he Department cannot, as has been requested by some, look for the single item of evidence which would qualify a claimant on the basis of the interim presumption, and ignore other previously obtained evidence. This does not mean that the single item of evidence which establishes the presumption is overcome by a single item of evidence which rebuts the presumption." Notice of Final Rulemaking under the Black Lung Benefits Reform Act of 1977, 43 Fed.Reg. 36826 (1978) (hereinafter Notice of Rulemaking) (emphasis added).

The Director's current position conflicts with this strong evidence of regulatory intent.

Another compelling reason to reject the Director's interpretation is that it conflicts with the requirement in part (b), the rebuttal section, that in "adjudicating a claim under this subpart, all relevant medical evidence shall be considered." § 727.203(b). The Director's interpretation turns the regulation on its head, requiring that all relevant medical evidence be submitted and weighed at the invocation stage, but severely restricting the consideration of medical evidence during the rebuttal stage. In the Director's view, the presumption is triggered only when the weight of evidence in one of the categories of medical evidence in part (a) proves the fact specified in that category. For instance, the "fact proved" under § (a)(1) is the existence of pneumoconiosis, and under § (a)(4) it is the presence of a totally disabling respiratory or pulmonary impairment. Because these facts have been proven in the invocation stage, relitigation in the rebuttal stage through like-kind evidence is foreclosed. Brief for Federal Respondent 14-15. Of course, nonmedical evidence could be presented in these instances, but this hardly conforms to the mandate that "all relevant medical evidence" be considered in the rebuttal stage.

The Court argues that the placement of the "all relevant medical evidence" requirement was inexact, and that the regulation requires only that all relevant medical evidence be considered at some point in the evaluation of a claim, whether it be during the invocation or rebuttal stage. Yet if the Secretary intended that the "all relevant medical evidence" language apply to both stages of the evaluation process, it is remarkable that he placed the language in the introduction to the rebuttal section. It would have been a simple matter, if such were the Secretary's intent, to place the "all relevant evidence" language at the beginning of § 727.200. I see no reason to assume such inartful drafting. Moreover, comments by the Secretary accompanying the final promulgation of the regulations conflict with the Court's interpretation. The Secretary stated: "The many comments which urge that all relevant evidence should not be considered in rebutting the interim presumption must also be rejected. . . . [T]he Social Security regulations . . . similarly do not limit the evidence which can be considered in rebutting the interim presumption." Notice of Rulemaking 36826 (emphasis added). These comments demonstrate that the Secretary understood the language to apply directly to the rebuttal section.

In addition, the Director's approach renders virtually useless one of four grounds for rebuttal in part (b). Under § (b)(4), eligibility for benefits is rebutted if all relevant medical evidence establishes that the miner does not have pneumoconiosis. Yet in the Director's view all relevant medicalevidence has already been considered at the presumption-invocation stage. It is only when the evidence presented during the invocation stage is mismatched, as for example when the claimant produces qualifying blood-gas-studies evidence and the mine operator produces negative X rays, that the presumption may be triggered and rebuttal evidence under § (b)(4) is available that has not already been weighed. Moreover, as the Director acknowledges, if a claimant invokes the presumption under § (a)(1) by a preponderance of X-ray, biopsy, or autopsy evidence, as a practical matter there is no further evidence that the coal mine operator could submit to rebut the presumed existence of pneumoconiosis because such (a)(1) evidence is the most reliable method of diagnosing the disease. See Brief for Federal Respondent 24, n. 22. The Court counters that "[n]othing in the regulation requires each rebuttal subsection to be fully available in each case." Ante, at 150. This is of course true. Yet it is extraordinary that the regulation would intend to make the rebuttal stage an often useless exercise with respect to the central aspect of a valid claim: whether a miner suffers from pneumoconiosis.

In addition to running afoul of the regulatory language and structure, the Director's reading of the regulation creates a needlessly complex regulatory scheme that blurs the distinction between the presumption-invocation and rebuttal stages. Under the Director's interpretation, when the weight of evidence in one of the medical-evidence categories invokes the presumption, then the same evidence cannot be considered during rebuttal to challenge the existence of the fact proved, but it may be considered if relevant to rebut one of the presumed elements of a valid claim for benefits. The Director's approach subjects the ALJ to a mesmerizing swirl of evidentiary rules. If the presumption is invoked under § (a)(1), then X-ray evidence may not be considered regarding the existence of pneumoconiosis, but may be considered, if relevant, on the issues whether the miner is totally disabled or whether the disease arose from coal mine employment. Similarly, if the presumption is invoked under § (a)(4), then medical evidence, including physicians' opinions, may not be considered on the issue of total disability, although it may be considered on the issues of the existence of pneumoconiosis and causation by coal mine employment. Finally, if the presumption is invoked using blood gas and ventilatory studies evidence under § (a)(2) and § (a)(3), the same evidence may be considered again regarding each rebuttal category, because the proved facts are not elements of a valid claim for benefits. The Director's interpretation thus creates a procedural morass that could not have been intended by the regulation's two-step inquiry.

By contrast, the Court of Appeals interpretation is marked by its simplicity. Under this approach the ALJ first determines whether the claimant has come forward with a qualifying medical test or physician's opinion and, if so, proceeds to the rebuttal stage. At this point all relevant evidence must be considered, and the mine operators may rebut the presumed existence of pneumoconiosis, total disability, and causation by coal mine employment on the basis of all the grounds provided by § 727.203(b).

The Court's willingness to accept the Director's interpretation of the regulation is based, I believe, on a misperception of the problem Congress and the Department of Labor were trying to alleviate with the interim presumption. Pneumoconiosis is an elusive and progressive disease. Congress was deeply concerned about the difficulty of diagnosing pneumoconiosis and the dearth of medical-testing facilities available to miners. Testimony before congressional committees and by Members of Congress repeatedly emphasized the unreliability of negative test results. As this Court stated in Usery v. Turner Elkhorn Mining Co., 428 U.S. 1, 31-32, and n. 33, 96 S.Ct. 2882, 2899-2900, and n. 33, 49 L.Ed.2d 752 (1976), "Congress was presented with significant evidence demonstrating that X-ray testing that fails to disclose pneumoconiosis cannot be depended upon as a trustworthy indicator of the absence of the disease," whereas there was no "authoritative indications that X-ray evidence of the presence of pneumoconiosis is untrustworthy."4 Juxtaposed with the difficulties in diagnosing pneumoconiosis was evidence that the disease was rife among long-term coal miners. Congressman Paul Simon noted one study that found that autopsies of 400 coal miners with more than 20 years' experience showed that 90-95% of them had pneumoconiosis. House Committee on Education and Labor, Black Lung Benefits Reform Act and Black Lung Benefits Revenue Act of 1977, 96th Cong., 282-283 (Comm.Print 1979). Testimony before the Senate estimated that as many as 50% of all coal miners will eventually become disabled from pneumoconiosis. See Hearings on S. 355 et al. before Subcommittee on Labor of the Senate Committee on Labor and Public Welfare, 91st Cong., 1st Sess., pt. 2, pp. 641, 856 (1969) (statements of Dr. I.E. Buff and Dr. Leon Cander).

The Court recognizes that Congress was especially concerned with the difficulties miners face in showing they suffer from pneumoconiosis. The Court reasons, however, that "Congress intended that those long-term miners who can show that they are truly diseased should have to prove no more. But if a miner is not actually suffering from the type of ailment with which Congress was concerned, there is no justification for presuming that that miner is entitled to benefits." Ante, at 158 (footnote omitted). Yet it is the difficulty in showing whether a miner is "truly diseased" that Congress found so troubling. No one disputes that the case file of a miner suffering from pneumoconiosis may include negative X rays, negative ventilatory studies, negative blood gas studies, and negative opinions by physicians. The interim presumption was designed to shift some of the risk of faulty test results from the miner to the employer. The evidence of high incidence of pneumoconiosis among long-term coal miners, coupled with the difficulties encountered in diagnosing the disease, gave the Department of Labor good reason for shifting this burden by presuming total disability due to pneumoconiosis based on findings of a single positive medical test or physician's opinion. The Director's current interpretation, which the Court today accepts, undermines that policy decision.

The Court is correct that the Agency's interpretation of its own regulations is entitled to deference. See, e.g., Bowles v. Seminole Rock & Sand Co., 325 U.S. 410, 414, 65 S.Ct. 1215, 1217, 89 L.Ed. 1700 (1945). But deference has its bounds. It is not a license for an agency effectively to rewrite a regulation through interpretation. An agency must abide by its regulations as written until it rescinds or amends them. See United States v. Nixon, 418 U.S. 683, 695-696, 94 S.Ct. 3090, 3101, 41 L.Ed.2d 1039 (1974). The Director's interpretation of the interim presumption is contrary to the plain language of the regulation, conflicts with comments of the Secretary accompanying the final promulgation of the regulation, and creates an unnecessarily complex regulatory scheme. Because I view the Agency's interpretation as plainly inconsistent with the regulatory language and history, I would not defer.

I accordingly dissent, and would affirm the judgment of the Court of Appeals.