Opinion for the Court filed by Circuit Judge WALD.
Dissenting Opinion filed by Circuit Judge MacKINNON:
WALD, Circuit Judge:Petitioner William Hensley appeals a decision and order of the Benefits Review Board of the United States Department of Labor which upheld a denial of his compensation claim brought under the Longshoremen’s and Harbor Workers’ Compensation Act (the “Act”), 33 U.S.C. § 901 et seq.1 Hensley claims a temporary, total disability due to psoriasis which, he alleges, was aggravated by his employment as a bus driver for the Washington Metropolitan Area Transit Authority (“WMATA”). An Administrative Law Judge found that the aggravation of Hensley’s pre-existing psoriatic condition was not work related. Appendix (“App.”) at 16-19. The Benefits Review Board, in a 2-1 decision, affirmed the finding of the Administrative Law Judge, holding that there was substantial evidence to support his decision. App. at 1-15. Because the Benefits Review Board and the Administrative Law Judge erred in evaluating the evidence before them, and therefore failed properly to apply the statutory presumption favoring the claimant in a case where no substantial evidence was presented to contradict his claim, the decision is reversed.
I. THE FACTS
Petitioner Hensley, husband and father of seven children, has been a bus driver for the past 33 years, employed for that entire period by respondent WMATA or its predecessor, D.C. Transit Authority. Since 1968 Hensley has been plagued by general psoriasis. Until August, 1977, however, his condition was well controlled by medication, and he never missed a day of work due to his skin condition. App. at 103. Hensley testified before the Administrative Law Judge that during June and July of 1977, his bus route came under construction, making the ride extremely rough.2 App. at 103-04. He further stated that the particular bus assigned to his route had very poor suspension, an uncomfortable driver’s seat, and a steering ratio requiring far greater effort for turns than other buses used by WMATA; all of this was acknowledged to be true by the Board. Id. at 3 n.3; 104-06. Hensley testified that he was therefore exposed to severe bouncing at certain points of contact, especially his left hand, the small of his back, the underside of his thighs, and his feet. Id. at 106-08.
[D]uring the course of this time my skin began to dry out and peel and crack; and it was very hard for me — in other words, it would hurt to hold the steering wheel. And I was trying to drive with a thumb and finger proposition [sic]. But when I would grip the wheel and be out there on the job for a while, then it would crack open and bleed from the work, from doing the job, from holding the steering wheel; it would actually crack open and my hand would bleed.
Id. at 108.
On August 15, 1977, Hensley ceased work on the advice of his treating physician, Dr. Donald Mitchell. Dr. Mitchell found peti*267tioner to be in severe pain and unable to use his hands and feet; his psoriasis was extensive with pustular lesions on the palms and the soles of his feet. App. at 30-3. Hensley was started on medication and he returned to work on August 23, 1977, despite advice from Dr. Mitchell that his condition would worsen if he began driving again. Id. at 49. But on September 5, 1977, Hensley was forced to stop work again due to the condition of his hands and feet, and he remained off work until November, 1978. Once Hensley stopped working, his condition stabilized. Id. at 111.
II. THE LAW
This court’s role in reviewing determinations of the Benefits Review Board under the Longshoremen’s Act is limited. We examine the record only to assure that the Board’s orders rest on substantial evidence on the record as a whole, and that the Board’s underlying standards for granting or denying compensation are in accord with the law. See Wheatley v. Adler, 407 F.2d 307, 310 (D.C.Cir.1968) (en banc). We have not hesitated, however, to reverse the Board’s orders when they fail properly to apply the Act’s presumption favoring claimants in disputed cases. See, e. g., Riley v. U. S. Industries/Federal Sheet Metal, Inc., 627 F.2d 455 (D.C.Cir.1980), cert. granted, 446 U.S. 941, 100 S.Ct. 2165, 64 L.Ed.2d 796 (1981); Swinton v. Kelly, 554 F.2d 1075 (D.C.Cir.), cert. denied, 429 U.S. 820, 97 S.Ct. 67, 50 L.Ed.2d 81 (1976); Wheatley v. Adler, supra.
The Act provides that compensation shall be payable when an employee covered under the Act suffers an “injury,” defined as “accidental injury ... arising out of and in the course of employment . . . . ” 33 U.S.C. § 902(2). Section 20 of the Act further provides that “[i]n any proceeding for the enforcement of a claim for compensation under this chapter it shall be presumed, in the absence of substantial evidence to the contrary — (a) That the claim comes within the provisions of this chapter.” 33 U.S.C. § 920 (emphasis supplied). The Section 20 presumption is but one indication of the “humanitarian nature” of the Act generally, O’Keefe v. Smith, Hinchman & Grylls Assoc., Inc., 380 U.S. 359, 362, 85 S.Ct. 1012, 1014, 13 L.Ed.2d 895 (1965), and the “beneficent purposes” which underlie it. Friend v. Britton, 220 F.2d 820, 821 (D.C.Cir.), cert. denied, 350 U.S. 836, 76 S.Ct. 72, 100 L.Ed. 745 (1955).
The presumption operates in favor of the claimant unless and until “substantial evidence” is presented by the respondent showing that the claimant’s malady did not arise out of and in the course of his employment. At that point, the presumption “falls out of the case.” Del Vecchio v. Bowers, 296 U.S. 280, 286, 56 S.Ct. 190, 193, 80 L.Ed. 229 (1935); Swinton v. Kelly, supra, 554 F.2d at 1082 n.35; Maryland Shipbuilding & Drydock Co. v. Jenkins, 594 F.2d 404, 407 (4th Cir., 1979); St. Louis Shipbuilding Co. v. Director, Office of Workers’ Compensation Programs, 551 F.2d 1119, 1124 (8th Cir., 1977); Travelers Insurance Co. v. Belair, 412 F.2d 297, 301 n.6 (1st Cir., 1969). This circuit has not decided whether, once the presumptive “bubble” bursts and falls out of the case, the ultimate burden of persuasion as to work-relatedness rests with the employer or employee. Cf. Parsons Corp. of California v. Director, Office of Workers’ Compensation Programs, 619 F.2d 38, 41 (9th Cir., 1980) (“Even after the substantial evidence is produced to rebut the statutory presumption, the employer still bears the ultimate burden of persuasion.”). But many courts, including our own, have decided that the beneficent purposes and humanitarian nature of the Act must be borne in mind when deciding whether the employer has presented “substantial” evidence; thus doubtful questions, including factual ones like work-relatedness, must be resolved in favor of claimants. Wheatley v. Adler, supra, 407 F.2d at 313-14 (“We have frequently pointed out that since the statute ‘should be construed liberally’ in favor of employees and their dependents, it is ‘in their favor [that] doubts, including the factual, are to be resolved.’ This approach has . . . characterized our application of the substantial evidence test *268in these cases.’’ [emphasis supplied]). See also Swinton v. Kelly, supra, 554 F.2d at 1084-85 (citing numerous cases); Ryan-Walsh Stevedoring Co. v. Trainer, 601 F.2d 1306, 1316 (5th Cir. 1979); Army & Air Force Exchange Service v. Greenwood, 585 F.2d 791, 794 (5th Cir., 1978); Bath Iron Works Corp. v. White, 584 F.2d 569, 574 (1st Cir., 1978); Young & Co. v. Shea, 397 F.2d 185, 188, rehearing en banc denied, 404 F.2d 1059, 1061 (5th Cir. 1968), cert. denied, 395 U.S. 920, 89 S.Ct. 1771, 23 L.Ed.2d 237 (1969) (“The policy of the Act that all doubtful questions are to be resolved in favor of the [claimant] is to be considered in determining whether there was substantial evidence before the Commissioner.” 404 F.2d at 1061). Applying this approach, this court has often found it necessary to reverse orders which are based on evidence too insubstantial to override the statutory presumption; we “will not sustain the administrative findings merely because they are substantiated by some isolated evidence.” Friend v. Britton, supra, 220 F.2d at 821. See, e. g., Swinton v. Kelly, supra, 554 F.2d at 1085 n.61 (collected cases decided in this circuit). On the contrary, in order to overcome the presumption, the employer’s “substantial evidence” must be “specific and comprehensive enough to sever the potential connection” between the disability and the work environment. Id. at 1083 (emphasis supplied); Parsons Corp. of California v. Director, Office of Workers’ Compensation Programs, supra, 619 F.2d at 41.
III. THE LAW APPLIED IN THIS CASE
It is uncontested that Hensley’s severely aggravated psoriasis condition is an “injury,” as that term is used in the Act; further, under the well recognized “aggravation rule” it is indisputable that “an aggravation of a pre-existing condition may constitute a compensable accidental injury under the Act[.]” Wheatley v. Adler, supra, 407 F.2d at 312. See Director, Office of Workers’ Compensation Programs v. Brandt Airflex Corp., 645 F.2d 1053, at 1057 (D.C.Cir.1981); Friend v. Britton, supra, 220 F.2d at 823; Robinson v. Bradshaw, 206 F.2d 435, 437 (D.C.Cir.), cert. denied, 346 U.S. 899, 74 S.Ct. 226, 98 L.Ed. 400 (1953); Ridgley v. Ceres, Inc., 594 F.2d 1175, 1177 (8th Cir. 1979). The fact that other, nonemployment related factors may also have contributed to, or additionally aggravated Hensley’s malady, does not affect his right to compensation under the “aggravation rule.” Cordero v. Triple A Machine Shop, 580 F.2d 1331, 1335 (9th Cir. 1978), cert. denied, 440 U.S. 911, 99 S.Ct. 1223, 59 L.Ed.2d 459 (1979); see Wheatley v. Adler, supra, 407 F.2d at 312 n.11 (“ ‘[T]he cases almost invariably decide that the fact that the injury would not have resulted but for the pre-existing disease, or might just as well have been caused by a similar strain at home or at recreation, are both immaterial.’ ”)
Thus, the only issue in this case is whether or not the aggravation of Hensley’s psoriasis, which occurred during July and August of 1977 when potholes and construction on his route made driving particularly stressful, arose even in part “out of and in the course of” his employment. 33 U.S.C. § 902(2). This statutory language
does not require “a causal relation between the nature of employment of the injured person and the accident.. .. All that is required is that the ‘obligations or conditions’ of employment create the ‘zone of special’ danger out of which injury arose.” .. . [The line is drawn] only at cases where an employee [has] become “so thoroughly disconnected from the service of his employer that it would be entirely unreasonable to say that injuries suffered by him arose out of and in the course of his employment.”
O’Keeffe v. Smith, Hinchman & Grylls Assoc., Inc., supra, 380 U.S. at 362, 85 S.Ct. at 1014 (emphasis supplied). See, e. g., Mitchell v. Woodworth, 449 F.2d 1097 (D.C.Cir. 1971) (denial of compensation reversed despite apparent absence of evidence that death arose from any particularly unusual work related stress); Butler v. District Parking Management Co., 363 F.2d 682 (D.C.Cir.1966) (denial of compensation re*269versed despite apparent absence of any particularized causal theory connecting claimant’s mental breakdown with his 20 years of service as a parking lot attendant); Robinson v. Bradshaw, supra (denial of death benefits reversed for failure to apply presumption to issue of work-relatedness in case where deceased suddenly became obsessed with idea that he was being pursued by mob, resulting in his confinement in jail, where he was thereafter fatally shot by police officer whom he attacked; presumption applied that his job as a truck driver aggravated some pre-existing mental illness).
In deciding whether the aggravation of Hensley’s psoriatic condition arose, even in part, out of and in the course of his employment as a bus driver, the factfinder was required to apply the Section 20 presumption in his favor. Swinton v. Kelly, supra, 554 F.2d at 1082 (“The statutory presumption applies as much to the nexus between an employee’s malady and his employment activities as it does to any other aspect of a claim.” Numerous cases cited); see Riley v. U. S. Industries/Federal Sheet Metal, Inc., supra, 627 F.2d at 458; Ridgley v. Ceres, Inc., supra, 594 F.2d at 1177.
Hensley’s allegation of work-relatedness, however, did not rest solely on the statutory presumption; on the contrary, he presented testimony on work-relatedness which overwhelmingly supported his claim. Hensley testified that after 32 years of driving a bus — 10 of them with chronic psoriasis but not a day’s work lost because of the condition — his psoriasis flared up so badly in the summer of 1977 that he was forced to quit work on his doctor’s advice. This was precisely the time when construction began on his route. He also testified that the lesions first appeared on those parts of his body where the physical trauma of driving was most concentrated, his left hand, his lower back and buttocks, and his right foot.3 App. at 106-08. While driving the bus his hands would “crack open and bleed . . . from holding the steering wheel.” Id. at 108. Then, when he stopped working, his condition improved; when he returned again, it worsened. All this was uncontra-dicted testimony, and by itself should have been sufficient evidence to show work-relatedness. See Eller and Co. v. Golden, 620 F.2d 71, 74 (5th Cir. 1980) (claimant’s own testimony may constitute substantial evidence justifying award of compensation under the Act).
In addition to Hensley’s testimony, however, two accredited dermatologists, one of whom was actually treating Hensley’s psoriasis at the time he had to stop work, stated that in their expert medical opinion the flare-up was, or certainly could have been, aggravated by Hensley’s driving a bus.4 The principal treating physician, Dr. *270Mitchell, testified that he advised Hensley at the time to stop working, warning that the condition would worsen if Hensley continued to drive. When Hensley persisted in staying on the job, the condition did worsen; when he finally stopped for good, it stabilized and improved somewhat. App. at 31-3, 36, 49, 111. Dr. Mitchell also corroborated many particulars of Hensley’s testimony, for example, that the pustular lesions on Hensley’s hands and feet were more severe than the lesions on the rest of his body,5 id. at 48, and that his left hand was more severely affected than his right, id. at 56.6
In sum, Dr. Mitchell’s overall testimony was consistent with at least two theories of work-related aggravation, namely, that pustular lesions appeared initially as a response to the physical trauma of driving, or that driving aggravated existing lesions to the point that they cracked, bled and made driving impossible. It is possible both things happened. In either case, work-related aggravation of an underlying psoriatic condition is clearly established on this record. It is, frankly, difficult for us to discern how the Administrative Law Judge and the Benefits Review Board could deny his claim based on this evidence, especially when the statute as construed by our court and others, see cases cited at pp. 267-268, 269, supra, presumes causality “in the absence of substantial evidence to the contrary.” 33 U.S.C. § 920.
We can find no substantial evidence to the contrary in this case. The only evidence adverse to Hensley that appears in the record is the testimony of Dr. Robert Stolar, hired by WMATA, who examined Hensley only once with regard to his claim. This examination took place nine months after the flare-up and eight months after he left work. The WMATA doctor’s conclusions were as follows:
In my experience the pattern of work that he carried on does not produce psori-atic lesions by the only known traumatic mechanism which I mentioned for the Koebner phenomena, which would require a different type of injury than what I could visualize that he received at any time.... So in attempting to visualize Mr. Hensley’s constant work pattern, his constant frictional pattern was of the smoothing or sliding variety, which is used very often as part of the treatment for psoriasis. So I could not visual*271ize that particular pattern of injury that would aggravate his condition.
App. at 73-4.7
This testimony does not constitute substantial evidence contradicting claimant’s theory of work-relatedness. The WMATA doctor’s “experience” that bus driving would not “produce psoriatic lesions” (emphasis supplied) in no way contradicts the claimant’s or his own doctors’ testimony that gripping the wheel and pressing the accelerator and brakes aggravated existing pustular lesions on his hands and feet to the point where he could not drive.8 Indeed the Board itself called the WMATA doctor’s testimony on this basic issue in the case “not crystal clear.” App. at 7.
More importantly, however, there is no evidence in the record that this third doctor had any particular experience or knowledge upon which to base his opinion regarding Hensley’s “work pattern” as a bus driver, or his opinion regarding the “constant frictional pattern” to which Hensley was subjected on his particularly rough bus route during July and August of 1977. Dr. Stolar, while an accredited dermatologist, was not shown tó have had any experience from which to estimate what sort of trauma Hensley was receiving from driving on his particular bus route, or which parts of the body received stress from such driving. At one point the Administrative Law Judge had to point this out:
Judge Giesey: Counsel, Dr. Stolar is an impressively credentialed member of a learned profession; but I do not think this is part of what he learned. I know as much about driving as the Doctor does...
App. at 84. Therefore, since this doctor’s ultimate opinion on work-relatedness was based entirely upon his “visualiz[ationj” of the kind of physical trauma involved in Hensley’s job, and since this “visualization]” was not derived from any particular experience or knowledge,9 we find that Dr. Stolar’s opinion on the issue of aggravation is not entitled to the “substantial” weight which it must have to overcome the Congressionally mandated presumption. Hensley’s claim should therefore have been sustained on the strength of that presumption, together with the evidence of his two treating physicians and his own testimony.
IV. THE DECISIONS OF THE ADMINISTRATIVE LAW JUDGE AND THE BENEFITS REVIEW BOARD
Given our conclusion that there was not “substantial” evidence to overcome the presumption of causality or the supporting evidence of claimant and his medical witnesses, we must conclude that the Administrative Law Judge erred in finding that “the weight of substantial evidence preponderate[d] on the side of non-exacerbation.” App. at 19. In fact, the Administrative Law Judge’s reasons for denying the claim are well nigh indecipherable to us. The *272Review Board itself admitted that his analysis was “not a model of clarity.” App. at 11 n.8. He reasoned thus:10
[T]he treating physician testified that Koebner’s phenomenon is produced only by injuries that penetrate the epidermis and injure the dermis but that “it’s well established that the mild, repeated trauma to the knees and elbows of patients accounts for the characteristic distribution of psoriasis, and this is a form of Keobner’s phenomenon.” Aside from the internal inconsistency of this testimony, photographs submitted in evidence with his report show that, while Hensley’s elbows have extensive psoriatic lesions, his knees are clear and uninvolved — despite the fact that his work is largely performed in a seated position and at least one leg, according to Hensley, “does all the work.” Ironically, this physician’s patient’s condition is significantly inconsistent with the premise upon which the entire theory of causation is based.
App. at 19. Our reading of the record reveals that the Administrative Law Judge badly misunderstood the import of the treating physician’s testimony. There is nothing whatsoever inconsistent in Dr. Mitchell’s conclusion that “mild, repeated trauma” which may come from “gripping a wheel of a bus” could produce a dermal injury likely to incite Koebner’s syndrome.11 Dr. Mitchell’s testimony was not only internally consistent, but it also significantly bolstered claimant’s theory of work-relatedness. The remainder of the Administrative *273Law Judge’s reasoning, which relies on the absence of aggravated psoriasis on Hensley’s knees, is simply irrelevant; Hensley’s claim was that his hands and feet, not his knees, were significantly involved in the driving.12 Thus the Administrative Law Judge’s final conclusion that Hensley’s condition was inconsistent with his “entire theory of causation” is simply a non sequitur.13
Although the Benefits Review Board in large part disclaimed reliance on the Administrative Law Judge’s reasoning, calling it “puzzling,” it concluded nevertheless that his reasoning did not “so undermine the . . . ultimate finding so as to require reversal.” App. at 11 n.8. Yet the Board itself engaged in equally murky thinking, relying on alleged facts which were irrelevant to the issue in this case, and failing to apprehend the thrust of the testimony on work-relatedness.
As to the former, the issue here has always been clear: whether the physical trauma of driving under unusually difficult circumstances contributed to the aggravation of Hensley’s already present psoriatic condition. The Board’s opinion, however, highlighted other factors such as obesity and emotional problems which could have contributed to the flare-up, App. at 6, though no one testified that they did so in fact. In this way the Board ignored decisions of this circuit and others, see p. 268, supra, which require a presumption in favor of job-relatedness where multi-causation may exist, and no substantial evi-deuce is introduced demonstrating that non-work related factors are the only causes. The Board also cited the fact that claimant had lesions on parts of his body not subjected to work pressure, i. e., his ankle and stomach. Such lesions are entirely consistent with the “capricious” nature of the disease — a flare-up in one portion of the body can, without apparent cause, spread to other parts. See n.3 supra. Finally, the Board relied upon the fact that the condition was still “severe” several months after he stopped driving, but ignored the undisputed evidence that his condition stabilized when he stopped driving the bus. See pp. 269-270 supra.
In addition to all this, the Board also apparently misunderstood the testimony concerning work-relatedness. Claimant testified that by gripping the wheel of the bus the psoriasis on his hands was traumatized to the point of bleeding. His physician, Dr. Mitchell, corroborated the testimony that he had pustular lesions on his hands and feet, App. at 30. These lesions constituted a dermal injury giving rise to a diagnosis of Koebner’s syndrome, one form of which occurs when “mild, repeated trauma” penetrates the dermal level of the skin causing a flare-up in the psoriatic patient’s condition. See App. at 34-5. Dr. Nigra’s statement was consistent with Dr. Mitchell’s regarding this causal scenario. See n.4 supra. But the Board chose to rely not upon this evidence, but instead upon the testimony of the WMATA doctor,14 and found that he *274“disagreed with Dr. Nigra’s opinion that trauma to an area of skin of a patient suffering from psoriasis will result in a flare of psoriasis in that area.” App. at 8. If the WMATA doctor’s testimony is so read by the Board, it is clear error. Medical texts on the disease recognize the fact that some kinds of trauma to the skin of a psoriatic patient may precipitate or aggravate the condition, see, e. g., 6 P. Cantor, Traumatic Medicine and Surgery for the Attorney 640-41 (1962) (“Chronic pressure caused by gripping tools may precipitate a psoriatic eruption of the palms. . . . The role of trauma in aggravating a pre-exist-ing psoriasis has to be accepted.”), and the WMATA physician acknowledged that fact as well. App. at 160.
Thus no testimony or evidence directly contradicted claimant’s theory of work-relatedness, that under unusually physically demanding driving, his psoriatic hands broke out in pustular lesions and then cracked and bled from gripping the wheel. This constituted work-related aggravation, and since there was no substantial evidence to contradict this causal scenario, while ample evidence existed to support it, the Board’s finding to the contrary is clearly erroneous.
V. CONCLUSION
Our review of the record here convinces us that both the Administrative Law Judge and the Benefits Review Board failed properly to apply the statutory presumption concerning work-relatedness in this case. There was no “substantial evidence” contradicting either the presumption or the considerable independent testimony by Hensley and his two doctors supporting the claim that his psoriatic condition was aggravated by driving a bus. The only witness who held the contrary opinion, that the aggravation was not work-related, based his conclusion on a wholly unsupported assumption concerning the actual working conditions under which claimant was laboring. The decision and order of the Board is therefore reversed, and the case remanded for an appropriate award in accordance with this opinion. Cf. Friend v. Britton, supra, 220 F.2d at 824.
So ordered.
. The Act’s provisions are applicable to employers in the District of Columbia pursuant to 36 D.C.Code § 501 et seq.
. Hensley testified, “[I]t just shook the heck out of your hands. It could even break your arm almost.” App. at 107.
. The dissent makes much of the fact that by the time the company’s doctor examined him nine months later, he had lesions all over his body. It is entirely consistent with the pattern of psoriasis that the emotional stress caused by the appearance of some lesions in one area precipitates lesions in other areas as well. Thus a person may simultaneously have some lesions that are a result of Koebner’s syndrome, j. e., caused or aggravated by physical trauma, see nn.4,11 infra, and others that are not. See generally 6 P. Cantor, Traumatic Medicine and Surgery for the Attorney 640--41 (1962).
. Dr. Mitchell stressed repeatedly in his deposition that he felt claimant’s underlying condition was aggravated by the conditions of his employment:
Q. Doctor, do you have an opinion that you can state with reasonable degree of certainty as to whether or not Mr. Hensley’s work as a bus driver aggravated his underlying condition of psoriasis?
A. Let me preface my statement by saying, I don’t think Mr. Hensley’s psoriasis is due to his driving a bus, but 1 certainly think that Koebner’s phenomenon plays a part in this, and that this is service-aggravated, as we used to call it in the Army.
Q. So his work did not cause the psoriasis but it certainly did aggravate the condition? A. Oh, yes.
App. at 31-2 (emphasis supplied).
Q. Let me ask just one or two more questions, Doctor. Then the occupation of driving a bus for this particular man, you think that his hands were affected by gripping the wheel?
A. Yes, that’s right.
Q. You mean by that that some of the roughening skin of the lesions on the hands were rubbed to some extent?
*270A. No, I think what occurred was this man — and in psoriasis, you can never generalize to every patient, because every patient with psoriasis is slightly different — I think the constant trauma of gripping and driving the bus made him worse.
Now, if he had been a carpenter, using a hammer and a saw, I think it would have gotten worse from using a hammer and a saw.
App. at 52 (emphasis supplied).
Q. I just have two questions, Doctor. Dr. Mitchell, you have testified that the constant trauma of gripping the steering wheel made Mr. Hensley’s condition worse?
A. Yes.
App. at 56 (emphasis supplied). See also Letter of Dr. Donald Mitchell, App. at 155 (“This condition is work aggravated as is demonstrated by the extensive psoriasis involving the palms and soles.”).
Dr. Thomas P. Nigra, M.D., to whom claimant was referred by Dr. Mitchell, said:
When I saw him, he had physically disabling psoriasis of his left hand. He is a Metro Bus driver, and there is little question that he uses his hands in his work.
Psoriasis is a capricious disease which waxes and wanes and comes and goes without cause. However, we definitely do know that trauma to an area of skin in a patient who has extensive psoriasis will result in a flare of psoriasis in the traumatic area. It is my opinion that using his hands in his work the way Mr. Hensley does as a bus driver could result in trauma and therefore flaring of his basic condition.
App. at 154.
. Contrary to the dissent’s contention, Diss. Op. at 2, pustular lesions are blister-like and Dr. Mitchell testified that gripping a wheel can cause blisters, and blisters, in turn, signify a dermal injury which can give rise to Koebner’s syndrome. See n. 11 infra.
. Hensley testified that he had to do most of the gripping of the wheel and steering with his left hand, while his right hand remained free to open and close doors and to service customers. App. at 101-02, 107.
. At the time he first examined him, Dr. Stolar wrote to the WMATA lawyer:
There is no question that Mr. William D. Hensley has an unfortunate and to a great extent disabling condition of psoriasis; however, in attempting to evaluate it from his history and examination, I was unable to determine that it was work related or work aggravated.
App. at 160 (emphasis supplied). Needless to say, the doctor’s inability to determine that Hensley’s condition was work-related does not satisfy the employer’s burden of showing with substantial evidence that his condition was not work-related.
. Ironically, Dr. Stolar testified that if Hensley had been his own patient, he too “probably would have stopped him from work long before, and tried to clear his skin.” App. at 83. But if Dr. Stolar really believed that work did not aggravate his condition, there would be no reason for such advice.
. The WMATA doctor’s “visualiz[ation]” of Hensley’s physical trauma as being “of the smoothing or sliding variety” was contradicted by the only witness whom the record shows had actual knowledge of the driving conditions: Hensley himself. If there was any question about Hensley’s description of the physical trauma he underwent on the route, surely it would have been incumbent upon WMATA to produce a witness to contradict that description. WMATA must be presumed to have at its disposal witnesses who can testify as to the stresses its drivers are subjected to on its bus routes.
. Prior to arriving at his “Findings of Fact and Conclusions of Law,” see text immediately infra, the Administrative Law Judge cited Hensley’s testimony that the streets on his route were “chopped all to pieces,” that the “bus assigned his route had notably poor suspension,” and that as a result “various parts of his body were ‘banged,’ ... he was ‘continually bouncing,’ and [the] driving ‘shook the heck out of [his] hands’....” App. at 17. The Law Judge then summarized the three doctors’ testimony, and concluded by noting that Dr. Stolar “stated ... that rubbing, smoothing or abrasion such as encountered in Hensley’s work is a part of the treatment for psoriasis, rather than an exacerbating influence.” Id. at 18. The Administrative Law Judge’s account of Dr. Sto-lar’s testimony appears to assume — as did Dr. Stolar — a “rubbing, smoothing” effect from driving that is completely at odds with Hensley’s first-hand account of what he was undergoing.
Furthermore, it is incorrect to assert that “rubbing, smoothing, or abrasion” per se constitutes a treatment for psoriasis, particularly if the “rubbing, smoothing or abrasion” is neither medically prescribed nor administered as in Hensley’s case. Dr. Stolar testified that one particular form of treatment for psoriasis involves using a polyester fiber sponge “to get rid of the scale, so that medication which is applied can be better absorbed and be much more effective.” App. at 75 (emphasis supplied); accord, App. at 35-6 (testimony of Dr. Mitchell). Since Hensley’s exposure to banging, bouncing and shaking was not part of any prescribed medical treatment involving medication and special sponges, his situation is far different from the one outlined in Dr. Stolar’s testimony.
. The Administrative Law Judge was probably referring to the following portion of Dr. Mitchell’s deposition:
Q. This Koebner’s syndrome or phenomenon of which you spoke a while ago, you used the illustration of a pin scratch, I believe.
A. Yes.
Q. Is that correct? And in order to produce this phenomenon, you must at least scratch below the first layer of skin, must you not?
A. Below'the first several layers of skin. You must go entirely through epidermis, and injur [sic] the dermis.
Q. So that simply gripping a wheel of a bus, using your hands in that manner, doesn’t produce scratches, does it?
A. Oh, haven’t you ever driven a car as much as I have? I have had blisters on my hands from driving an automobile. I had a little sports car; I had to change the steering wheel because it produced blisters every time I drove the thing....
Q. That produced blisters, but it didn’t cut your hands, did it?
A. No, but when you produce a blister, you have got a dermal problem.
App. at 40-1. Needless to say, this testimony is not at all inconsistent with another illustration of the Koebner phenomenon which Dr. Mitchell provided at another point in his deposition: that “it’s well established that the mild, repeated trauma to the knees and elbows of patients accounts for the characteristic distribution of psoriasis, and this is a form of Koeb-ner’s phenomenon.” Id. at 35. In fact. Dr. Mitchell’s testimony was clear and unambiguous on the issue of whether the aggravation of Hensley’s psoriasis was work-related. See n.4 supra.
. The Board itself admitted that the Administrative Law Judge’s “stressing of the fact that claimant’s knees were not affected by psoriasis is puzzling in light of the fact that claimant’s knees did not appear to be subject to repeated trauma.” App. at 11 n.8.
. There is little doubt in our minds that even if the Administrative Law Judge had entirely ignored the statutory presumption, he would still have had to find that the weight of the medical evidence was in Hensley’s favor, since the testimony of two treating physicians is normally entitled to greater weight than the testimony of one physician who examines the claimant only once, many months later, in connection with the claim. See generally Combs v. Gardner, 382 F.2d 949, 956-57 (6th Cir. 1967); Shaw v. Harris, Civ. No. 79-869 (D.D.C., Nov. 6, 1979) at 5 (“as a matter of law the testimony in evidence of a doctor who treats a patient over a substantial period of time is entitled more consideration than the testimony of a doctor who examined a patient once.”); see also Robinson v. Richardson, 360 F.Supp. 243, 250 (E.D.N.Y.1973); Claussell v. Secretary of HEW, 337 F.Supp. 717, 722 (S.D.N.Y.1972); Teague v. Gardner, 281 F.Supp. 43, 48 (E.D.Tenn.1968).
. The Board quoted Dr. Stolar’s letter to WMATA which stated in part:
Psoriasis has so many spontaneous increases and decreases, and lesions, and extent [sic] that it is impossible to determine that any one pattern of injury may definitely be the responsible agent for its manifestations.
*274App. at 10. This concession by Dr. Stolar, the employer’s only witness, would seem to rule out the notion that he could say work was not a responsible agent. If he could not, then the presumption of work-relatedness applies.