dissenting.
I respectfully dissent. The disputed regulatory language is complex, but it is not ambiguous, and I do not think Chevron deference, see Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837 (1984), requires us to accept the strained and implausible construction advanced by the Department of Labor (DOL). In my judgment at least one of the claimants before us is entitled to benefits under the statute.
*707I — I
A
As an initial matter, the Court misconstrues our Chevron jurisprudence. Chevron requires that we defer to an agency’s interpretation of its organic statute once we determine that that statute is ambiguous. No one contends that the relevant statutory language (“shall not be more restrictive than”) is ambiguous. See Pittston Coal Group v. Sebben, 488 U. S. 105, 113-114 (1988) (explaining that particular phrase). The only serious question surrounds the regulations of the then-extant Department of Health, Education, and Welfare (HEW) to which the statute refers. I agree that those regulations are complex, perhaps even “Byzantine,” ante, at 699 — but that alone is insufficient to invoke Chevron deference. Deference is appropriate where the relevant language, carefully considered, can yield more than one reasonable interpretation, not where discerning the only possible interpretation requires a taxing inquiry. Chevron is a recognition that the ambiguities in statutes are to be resolved by the agencies charged with implementing them, not a declaration that, when statutory construction becomes difficult, we will throw up our hands and let regulatory agencies do it for us. In my view the HEW regulations referred to by the present statute are susceptible of only one meaning, although they are so intricate that that meaning is not immediately accessible.
But even if the regulations were ambiguous, it would not follow that the Secretary of Labor is entitled to deference. Nothing in our Chevron jurisprudence requires us to defer to one agency’s interpretation of another agency’s ambiguous regulations. We rejected precisely that proposition in Martin v. Occupational Safety and Health Review Comm’n, 499 U. S. 144 (1991), in holding that the Occupational Safety and Health Review Commission (OSHRC) was not entitled to deference in interpreting the Secretary of Labor’s regulations. Having used Chevron to rebuff OSHRC’s incursions *708there, it seems a bit greedy for the Secretary to use Chevron to launch the DOL’s own cross-border attack here. In my view, the only legitimate claimant to deference with regard to the present regulations is the agency that drafted them.
B
In any event, the interpretive issue here is, in my view, much less difficult than the Court suggests. Title 30 U. S. C. § 902(f)(2) states: “Criteria applied by the Secretary of Labor ... [to black lung claims filed prior to April 1, 1980,] shall not be more restrictive [i. e., shall not be less favorable to claimants] than the criteria applicable to a claim filed on June 30, 1973.” The criteria applied by the Secretary of Labor are as follows:
Ҥ727.203 Interim Presumption.
“(a) Establishing interim presumption. A miner who engaged in coal mine employment . . . will be presumed to be totally disabled due to pneumoconiosis . . . if one of the following medical requirements is met:
“(1) A chest roentgenogram (X-ray), biopsy, or autopsy establishes the existence of pneumoconiosis (see §410.428 of this title);
“(2) Ventilatory studies establish the presence of a chronic respiratory or pulmonary disease . . .
“(3) Blood gas studies . . . demonstrate the presence of an impairment in the transfer of oxygen from the lung alveoli to the blood . . .
“(4) Other medical evidence . . . establishes the presence of a totally disabling respiratory or pulmonary impairment;
“(b) Rebuttal of interim presumption. In adjudicating a claim under this subpart, all relevant medical evidence shall be considered. The presumption in paragraph (a) of this section shall be rebutted if:
*709“(1) The evidence establishes that the individual is, in fact, doing his usual coal mine work or comparable and gainful work (see § 410.412(a)(1) of this title); or
"(2) In light of all relevant evidence it is established that the individual is able to do his usual coal mine work or comparable and gainful work (see § 410.412(a)(1) of this title); or
“(3) The evidence establishes that the total disability or death of the miner did not arise in whole or in part out of coal mine employment; or
“(4) The evidence establishes that the miner does not, or did not, have pneumoconiosis.” 20 CFR §727.203 (1990).
The criteria governing claims filed on June 30, 1973, were set forth in HEW interim regulations, 20 CFR § 410.490, which provide in relevant part:
“(b) Interim presumption. With respect to a miner who files a-claim for benefits before July 1, 1973, . . . such miner will be presumed to be totally disabled due to pneumoconiosis ... if:
“(1) One of the following medical requirements is met:
“(i) A chest roentgenogram (X-ray), biopsy, or autopsy establishes the existence of pneumoconiosis (see §410.428); or
“(ii) In 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 . . .
“(2) The impairment established in accordance with paragraph (b)(1) of this section arose out of coal mine employment (see §§410.416 and 410.456).
“(c) Rebuttal of Presumption. The presumption in paragraph (b) of this section may be rebutted if:
*710“(1) There is evidence that the individual is, in fact, doing his usual coal mine work or comparable and gainful work (see § 410.412(a)(1)), or
“(2) Other evidence, including physical performance tests . . . establish that the individual is able to do his usual coal mine work or comparable and gainful work (see § 410.412(a)(1)).”
The relationship between the two regulations is apparent because they use a similar structure and, in large part, similar language. Both allow claimants to invoke a presumption of disability due to pneumoconiosis upon the presentation of certain medical evidence (the HEW regulations provide for two types of medical evidence while the DOL regulations provide for four). Both specify certain ways in which that presumption may be rebutted. The HEW regulations, however, specify only two methods of rebuttal (both relating to the extent of the disability), while the DOL regulations authorize four methods (the two expressed in the HEW regulations plus two more: (1) that pneumoconiosis did not cause the disability, and (2) that the miner does not have pneumoconiosis).
Obviously, if the DOL regulations provide more opportunities for rebuttal, they are less favorable to claimants. I think it quite apparent that they do. The present case is illustrative. Claimant Pauley invoked the presumption by submitting X-ray evidence of pneumoconiosis, pursuant to § 727.203(a)(1). BethEnergy, the employer, rebutted the presumption by arguing pursuant to § 727.203(b)(3) that although Pauley had pneumoconiosis it did not cause his disability. Had the case proceeded under the HEW regulations, Pauley’s presentation would have been the same, under § 410.490(b)(l)(i), the counterpart of § 727.203(a)(1).1 *711For BethEnergy, however, things would have been different: § 727.203(b)(3) does not have a counterpart in the HEW regulations. The only rebuttal expressly contemplated by the HEW regulations is that the claimant is not in fact disabled— but Pauley concededly was. It appears, therefore, that BethEnergy could not have challenged the causal link between the pneumoconiosis and the disability under the HEW regulations and thus would have had no defense.
In my view this argument is self-evidently correct and is obscured only by the technical complexity of the regulatory provisions. But the statutory structure, as opposed to the actual language, is simple. Under the HEW regulations, we assume “x,” but “x” may be rebutted by a showing of “a” or “b.” Under the DOL regulations, we likewise assume “x,” but “x” may be rebutted by a showing of “a” or “b” or “c” or “d.” It defies common sense to argue that, given this structure, the two regulations are in fact identical, and that Pauley, whose claim could be defeated by a showing of “c” but not by a showing of “a” or “b,” was no worse off under the latter regime. Yet that is precisely the argument the Court accepts.
Pauley’s commonsense reading is further supported by the fact that there is nothing remarkable about the HEW regulations’ severely limiting rebuttal. The introduction to those regulations states:
“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 pneumo-coniosis, and that such claims must be handled under *712present 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 . . . § 410.490(a).
In this context, the limitation on rebuttal makes perfect sense. Litigation over the existence of pneumoconiosis was circumscribed: If the claimants introduced specified types of medical evidence supporting their claim, that portion of the case would be deemed established — thus avoiding the time-consuming exchange of conflicting medical evidence which, given the technology and scientific knowledge then available, was likely to be inconclusive in any event. Similarly, litigation over the causal link between the disease and the disability — which poses even more difficult medical questions — was eliminated entirely by the presumption that if a miner had pneumoconiosis and was disabled, he was disabled because of pneumoconiosis. On the other hand, the regulations permitted full litigation as to the existence of a disability, an area where medical and scientific knowledge was equal to the task and where agencies (and courts) typically think themselves able to make reasoned assessments.2
In addition, apparently the interim regulations were at the time thought to limit rebuttal. Literally thousands of cases were decided pursuant to these regulations in the 1970’s; neither the Government nor the employers have cited a single *713instance in which the rebuttal allowed by the DOL regulations was permitted or indeed was even advanced, nor have they cited a single comment by the Secretary of HEW, any claimant, or any commentator suggesting that such rebuttal was available. I do not find that extraordinary. In my view that is the only reasonable reading of the regulations, and it is unsurprising that no one thought to read them otherwise. Indeed, that is precisely how we read them in Pittston Coal. Although the question was not specifically before the Court, in generally describing the two sets of regulations, we stated:
“[T]he rebuttal provisions of the interim Labor regulation . . . permi[t] rebuttal not only on the grounds available in the interim HEW regulation (§ 410.490(c)), but also on the basis that ‘the total disability or death of the miner did not arise in whole or in part out of coal mine employment’ or that ‘the miner does not, or did not, have pneumoconiosis.’ See §§ 727.203(b)(1)-(4).” 488 U. S., at 111 (emphasis added).
hH I — 1
Although I think the HEW regulations clear (albeit complex) on their face, I turn now to the specific arguments why they should nevertheless not be read to limit rebuttal opportunities.
A
First, the Government contends that the HEW rebuttal provisions actually include the two new rebuttal provisions apparently added by DOL. The principal claim here centers upon subsection (b)(2) of the HEW regulations. That provision states that the claimant must demonstrate that the “impairment established in accordance with paragraph (b)(1) of this section arose out of coal mine employment.” 20 CFR § 410.490(b)(2) (1990). This requirement, the Government insists, is comparable to DOL’s third rebuttal provision, which permits the employer to show that the miner’s disabil*714ity did not arise from coal mine employment. That argument might be correct if “impairment” in subsection (b)(2) of the HEW regulations meant the same as “disability” in the DOL regulations. It does not. Subsection (b)(2) of the HEW regulations refers to the. “impairment” established in subsection (b)(1); that subsection discusses proof of the existence of pneumoconiosis. The (b)(2) “impairment,” then, is the disease itself. Thus, it is open to the employer under the HEW regulations to show, for example, that Pauley’s pneu-moconiosis did not arise from coal mine employment. But here everyone agrees that it did — the relevant question is whether Pauley’s disability arose from his pneumoconiosis. That is where DOL diverges from HEW, for DOL’s regulations allow proof that the disability did not arise from the disease and thus from coal mine employment; the HEW regulations require only a showing that the impairment — i. e., the pneumoconiosis — arose from coal mine employment and presume the causal link between the impairment and the disability.
The Government contends that subsection (b)(2) of the HEW regulations also equates with the fourth rebuttal provision of the DOL regulations. The fourth rebuttal provision allows rebuttal on the ground that the claimant does not have pneumoconiosis. I think the Government’s argument is partially correct — but only partially. As the Government notes, proof of pneumoconiosis involves proof of two elements: (1) a chronic dust disease, which (2) arose from coal mine employment. Subsection (b)(1) of the HEW regulations says the claimant must prove the first point, and says how to do it (by submitting the specified medical evidence and thereby raising the presumption). Subsection (b)(2) says that the claimant must also prove the second point (to which the presumption is irrelevant). To contest a finding of pneumoconiosis, the employer may wish to argue either (1) that the miner has a chronic dust disease but it did not arise from coal mine employment; or (2) that the miner does not have a chronic dust *715disease. Subsection (b)(2) of the HEW regulations allows the employer to argue the former, but it says nothing about the latter; and subsection (b)(1) bars the latter argument, via the presumption, if the miner offers the specified medical evidence. DOL’s fourth rebuttal allows the employer to argue either point — and thus, impermissibly, offers additional recourse to the employer.
The employers offer yet another contortion of the statute to the same effect. Section 410.490(c) states that rebuttal may be made through “evidence that the individual is, in fact, doing his usual coal mine work or comparable and gainful work (see § 410.412(a)(1)).” The provision incorporated by reference reads as follows:
“(a) A miner shall be considered totally disabled due to pneumoconiosis if:
“(1) His pneumoconiosis prevents him from engaging in gainful work in the immediate area of his residence requiring the skills and abilities comparable to those of any work in a mine or mines in which he previously engaged with some regularity and over a substantial period of time
Because this provision begins with references to the miner’s disability due to pneumoconiosis, the employers believe it would be reasonable to construe it as authorizing the argument either that the miner does not have the disease or that the disease is not causing the disability. I do not find this a plausible explanation of the reference to § 410.412(a)(1). The logical reason for cross-referencing that provision was to include within the explicit rebuttal provision the more complete definition of “gainful work” that the incorporated section affords. Had HEW intended to create additional rebuttal provisions, it would simply have done so, explicitly and in parallel with the other rebuttal provisions, rather than backhandedly, through the incorporation by reference.
The Court apparently concedes that the companies’ cross-reference argument is not the most natural reading of the *716statute, but concludes that “the Secretary’s view need be only reasonable to warrant deference.” Ante, at 702. While I do not even think the foregoing argument reasonable (nor do I think the Secretary entitled to deference, see supra, at 707-708), I note that the Secretary herself does not advance it. Certainly private parties’ speculation as to what the Secretary could have thought warrants no deference.
B
The Government’s second line of attack centers upon its claim that the HEW regulations, if read to limit rebuttal, would violate the Black Lung Benefits Act of 1972. That argument has potential force, for we are more willing to depart from the natural import of language when adhering to it would render a regulation unauthorized or a statute unconstitutional. It is important to note at the outset, however, that the Government has a heavy burden in this regard. Had the HEW regulations been challenged before this Court as inconsistent with the statute, we would have owed Chevron deference to the Secretary (of HEW). The Government’s present argument depends on a showing, not that a natural reading of the HEW regulations produces less than the best reading of the statute, but that it produces an unreasonable one.
The Government argues, and the Court accepts, that “it disserves congressional intent to interpret HEW’s interim regulations to allow recovery by miners who do not have pneumoconiosis or whose total disability did not arise, at least in part, from their coal mine employment,” ante, at 700, and thus HEW must have permitted rebuttal on these grounds even if its regulations did not say so. I think that most unlikely. Any adjudication of claims necessarily involves a tradeoff between the speed and the accuracy of adjudication. As discussed above, the HEW presumptions were avowedly designed to enhance speed at the expense of accuracy, see § 410.490(a), pending the development of more *717reliable procedures. As with all presumptions, their preclusion of full litigation of some issues left open the possibility that some claimants would receive benefits to which, in a perfect world, they would not be entitled. That is a necessary consequence of attempting to resolve complex and possibly indeterminate claims with a minimum of delay. I cannot say that in striking such a balance HEW violated a clear policy of Congress, for Congress itself had taken up the black lung issue in 1972 in part because of a perception that adjudication of claims was moving too slowly.
It is next argued that certain specific provisions of the authorizing statute mandate the methods of rebuttal later adopted by DOL. Specifically, according to the Court, “the authorizing statute . . . expressly provides that the presumptions in question will be rebuttable, see 30 U. S. C. §§ 921(c) (1), (2), and (4), and requires the Secretary of HEW to consider all relevant evidence in adjudicating claims .... See 30 U. S. C. § 923(b).” Ante, at 702-703. I see nothing in § 921, however, that contradicts HEW’s limitation on rebuttal. Section 921(c)(1) provides: “If a miner who is suffering or suffered from pneumoconiosis was employed for ten years or more in one or more coal mines there shall be a rebuttable presumption that his pneumoconiosis arose out of such employment.” That provision is simply irrelevant to the issue of whether rebuttal must be allowed as to either the existence of pneumoconiosis or the causal link between the disease and the disability. The HEW regulations do not purport to establish an irrebuttable presumption relating to the link between the disease and employment in coal mines.
Slightly more on point is § 921(c)(2), which provides: “If a deceased miner was employed for ten years or more in one or more coal mines and died from a respirable disease there shall be a rebuttable presumption that his death was due to pneumoconiosis.” It is plausible to read that section as foreclosing HEW from establishing an irrebuttable presumption of causation based solely on death after 10 years’ service. *718But that is not what the HEW regulations do. Rather, they establish an irrebuttable presumption based upon 10 years’ service plus substantial additional medical evidence. It is not inconsistent to say that certain evidence establishes a rebuttable presumption and additional, more persuasive evidence establishes an irrebuttable presumption.
Section 921(c)(4) is the most relevant, for it establishes a presumption of disability based upon a showing of pneumoco-niosis. It then states in relevant part that “[t]he Secretary may rebut such presumption only by establishing that (A) such miner does not, or did not, have pneumoconiosis . . . .” (Emphasis added.) It is true that this rebuttal provision tracks the fourth rebuttal provision of the DOL regulations. However, § 921(c)(4) is permissive. It establishes the ways in which the Secretary may rebut a presumption but does not require that the Secretary use them. It is not inconsistent with the statute for the Secretary to decide that such rebuttal attempts would involve more administrative expense than they could justify and thus to adopt regulations declining to exercise the option.
In my view, the only colorable claim to a statutory conflict is based on § 923(b), which provides in part that “[i]n determining the validity of claims under this part, all relevant evidence shall be considered.” The Government argues with some force that this precludes the use of presumptions that do not allow the introduction of all relevant evidence. That is an unanswerable argument with respect to evidence offered by the claimants. I think it reasonably maintainable, however, that the preclusion does not apply to evidence offered against them. At the time the interim regulations were adopted, HEW, not the employers, paid the benefits required under the Act. In adopting its presumptions, HEW was limiting the evidence it could offer to sustain its own position. The presumption provisions were, in effect, a waiver — which may well have been based upon compelling considerations of administrative efficiency. I think the stat*719ute is at least ambiguous as to whether the Secretary could elect not to contest claims based on certain evidence. Since we owe the Secretary (of HEW) Chevron deference in construing the statute, I cannot say that, if the Secretary had taken that position (as he apparently did in promulgating the regulations), we would not have accepted it as a permissible interpretation.
C
The Government’s final argument is that the HEW regulations do not expressly preclude rebuttal on grounds other than those specified. Thus, even if expanded rebuttal is not specifically provided for, neither is it foreclosed; the statute adopting the HEW regulations is simply ambiguous as to its availability, and we should defer to DOL’s view that it should exist. It is true that the HEW regulations do not say that these are the only two ways to rebut the presumption. That is, however, the reasonable implication, as is suggested by the hoary canon of construction, expressio unius est exclusio alterius. When a provision sets forth a general rule followed by specific exceptions to that rule, one must assume — absent other evidence — that no further exceptions are intended. The Court argues that the principle of expressio unius is not absolute, and may be rejected where its application “would render a regulation inconsistent with the purpose and language of the authorizing statute.” Ante, at 703. That is assuredly true; it is only one of many possible indications of meaning. Cf. Burns v. United States, ante, at 136-138 (invocation of expressio unius inappropriate where it would lead to absurd and arguably unconstitutional results). It is a strong indication, however, and the problem here is that there are no others. As discussed above, limitation of rebuttal is not contrary to the text or purpose of the authorizing statute, and neither the Government nor the Court offers any other reason for thinking that the listed exceptions are not exclusive.
*720H — I H — I HH
In sum, the DOL regulations impermissibly exceed the HEW regulations in at least two respects: (1) they allow employers to argue that a miner who has pneumoconiosis and is disabled is nevertheless not disabled due to the pneumoconio-sis, and (2) where a miner has submitted specified evidence of a chronic dust disease, they allow the employer to challenge not only whether the disease is coal related, but whether the disease exists. That was the view of these regulations we expressed in Pittston Coal, see 488 U. S., at 111, and I see no reason to reconsider.3 As to claimant Pauley, that divergence is conclusive, at least as far as the statute is concerned. (I do not address constitutional challenges to the statute, as these were not passed upon below.) The employer’s only defense was that Pauley’s pneumoconiosis was not the cause of his disability, and that defense was foreclosed under the HEW regulations. Thus, I would reverse in No. 89-1714. Claimant Dayton presents a more difficult case. He submitted ventilation studies showing a disease resembling pneumoconiosis. The employer wishes to argue that he does not have pneumoconiosis. As I read the regulations, the employer may not challenge the conclusion that Dayton has a pneumoconiosis-like disease, but may (depending upon the effect of other provisions not argued here) claim that the disease did not arise from coal mine employment. Since it is not clear on the present record which of these positions the employer is advocating, I would remand in No. 90-114. Finally, I agree with the Court that claimant Taylor is entitled to no relief. Taylor invoked the presumption of disability via a blood gas test, § 727.203(a)(3). That was not an approved method of invoking the presumption under the HEW regulations. Taylor cannot complain that DOL has treated him less well than HEW would have in allowing the *721presumption to be rebutted, since under the HEW regulations he would not have been entitled to the presumption in the first place. Accordingly, I would reverse in No. 90-113.
For the foregoing reasons, I respectfully dissent.
The HEW regulations also contain a separate provision that would have required Pauley to show that his medical condition arose from working in a coal mine. § 410.490(b)(2). While that requirement is not set forth as a separate provision in the DOL regulations, it is presumably a *711part of § 727.203(b)(4), which requires that the miner have pneumoconiosis. Pneumoconiosis is specifically defined as a disease arising from work in a coal mine. 30 U. S. C. § 902(b). It is not contested that Pauley’s pneu-moconiosis arose from work in the mine — only that it, rather than his other ailments, was the cause of his disability.
In its permanent regulations HEW did not use the §410.490 interim presumption. Significantly, the permanent regulations also outlined an extensive procedure for contesting the link between a miner’s pneumoconiosis and his disabilities. See § 410.426. The fact that this provision was not contained in the interim procedures suggests that HEW thought disability causation would not be an issue there — and conforms to the view, see § 410.490(a), that the interim presumptions would serve as a blunt instrument for adjudication until full evidentiary procedures could be developed.
Even if the Secretary of Labor were the proper party to claim Chevron deference in interpreting these regulations, I find her arguments to the contrary so implausible that I would not accept them in any event.