Opinion by Judge TASHIMA; Dissent by Judge TROTT.

OPINION

In this action under the Americans with Disabilities Act of 1990, 42 U.S.C. § 12101 et seq. (“ADA”), we held in an earlier opinion that the “direct threat” defense provided by 42 U.S.C. § 12113 in an ADA discrimination action does not include threats to the employee’s own health. *1026 Echazabal v. Chevron U.S.A., Inc., 226 F.3d 1063, 1070 (9th Cir.2000). In Chevron U.S.A. Inc. v. Echazabal, 536 U.S. 73 , 122 S.Ct. 2045 , 153 L.Ed.2d 82 (2002) (“Echazabal ”), the Supreme Court reversed and remanded, holding that the direct threat defense includes threats to an employee’s own health. It also held the EEOC’s direct threat regulation, 29 C.F.R. § 1630.15 (b)(2) (defining the defense to include threats to the employee), to be valid. Id.

In light of Echazabal, the only remaining issue on remand is whether Chevron has met the requirements for assertion of the direct threat defense. Specifically, we must decide whether Chevron based its decision upon “ ‘a reasonable medical judgment that relies on the most current medical knowledge and/or the best available objective evidence,’ and upon an expressly ‘individualized assessment of the individual’s present ability to safely perform the essential functions of the job,’ reached after considering, among other things, the imminence of the risk and the severity of the harm portended.” Echazabal, 122 S.Ct. at 2053 (quoting 29 C.F.R. § 1630.2 (r) (2001)). We conclude that, on summary judgment, material issues of fact remain; therefore, the district court erred in granting summary judgment to Chevron. We reverse and remand for further proceedings.

FACTUAL BACKGROUND

Between 1972 and 1996, Mario Echaza-bal worked for a variety of maintenance contractors at Chevron’s oil refinery in El Segundo, California, primarily within the coker unit. In 1992, Echazabal applied to work directly for Chevron in the same coker unit. Chevron extended to him an offer of employment, contingent on his passing a physical examination. An examination by Chevron’s physician revealed that Echazabal’s liver was releasing higher than normal levels of enzymes. Chevron concluded that Echazabal’s health might be at risk from exposure to chemicals present in the coker unit and rescinded its offer. Echazabal continued to work at the refinery as an employee of Irwin Industries, Inc., a maintenance contractor for Chevron.

After learning of these test results, Echazabal consulted with his own doctors and was eventually diagnosed with asymptomatic, chronic active hepatitis C. Throughout his treatment, Echazabal informed his personal physicians about the work he continued to perform at the refinery. None of the physicians advised him to cease working there.

In 1995, Chevron again offered Echaza-bal a job, contingent on passing a physical examination. Echazabal had the physical examination Chevron requested in January 1996. Shortly thereafter, he received a letter, dated February 6, 1996, informing him that Chevron was withdrawing the job offer based on its determination that Echa-zabal’s liver would be damaged and his health at risk if he worked at the coker unit. Prior to the receipt of this letter, Echazabal had not received any indication that the offer might be withdrawn, nor had he been given any opportunity to demonstrate that he could safely perform the job. 1 Unlike the previous time that Chev *1027 ron withdrew its job offer, this time Chevron also asked Irwin to remove Echazabal from the refinery or place him in a position that would eliminate his exposure to solvents or chemicals. As a result, Echazabal lost his position with Irwin at the El Segundo refinery, which also caused him to lose his medical insurance coverage. Consequently, he was no longer able to pay for medical services and was unable to continue with the medical group he had been seeing for his liver condition.

ANALYSIS

An employer can defend against a disability discrimination claim under the ADA by relying on a qualification standard that “is shown to be job-related for the position in question and is consistent with business necessity.” 42 U.S.C. § 12112 (b)(6). Such a qualification standard “may include a requirement that an individual shall not pose a direct threat to the health or safety of other individuals in the workplace.” 42 U.S.C. § 12113 (b). The statute further provides that “[t]he term ‘direct threat’ means a significant risk to the health or safety of others that cannot be eliminated by reasonable accommodation.” 42 U.S.C. § 12111 (3). Because it is an affirmative defense, the burden of establishing a direct threat lies with the employer. Hutton v. Elf Atochem N. Am. Inc., 273 F.3d 884, 893 (9th Cir.2001); Nunes v. Wal-Mart Stores, Inc., 164 F.3d 1243, 1247 (9th Cir.1999).

Before excluding an individual from employment as a direct threat, an employer must demonstrate that it has made an “individualized assessment” of the employee’s ability to perform the essential functions of the job, “based on a reasonable medical judgment that relies on the most current medical knowledge and/or on the best available objective evidence.” 29 C.F.R. § 1630.2 (r). The factors to be considered include: “(1) The duration of the risk; (2) The nature and severity of the potential harm; (3) The likelihood that the potential harm will occur; and (4) The imminence of the potential harm.” 2 Id. The Supreme Court emphasized the requirement of a “particularized enquiry into the harms the employee would probably face.” Echazabal, 122 S.Ct. at 2053 .

A. The “individualized assessment” requirement

Chevron defends its assessment disqualifying Echazabal from employment with three arguments: (1) It satisfied the individualized assessment requirement by relying on the “facially proper” opinions of “competent physicians.” (2) There were no genuine issues of material fact with regard to the four Arline factors. (3) The opinions of Echazabal’s medical experts cannot be considered in evaluating its employment decision because they were made “long after the fact.”

*1028 1. The standard for evaluating medical judgments

Chevron argues that its reliance on the advice of its own doctors, and allegedly upon that of Echazabal’s doctors, constitutes a “facially reasonable” and thus a legally sufficient “individualized assessment” of Echazabal. This is an erroneous interpretation of the governing standard. 3 The regulation presents a much more specific matrix against which to measure the reasonableness of the employer’s action:

29 C.F.R. § 1630.2 (r).

In Bragdon v. Abbott, 524 U.S. 624 , 118 S.Ct. 2196 , 141 L.Ed.2d 540 (1998), the Supreme Court considered a direct threat defense presented by a dentist concerned about treating an HIV-infected patient. The Court stated that the health care provider had a duty to assess the risk based on “the objective, scientific information available to him and others in his profession.” Id. at 649 , 118 S.Ct. 2196 . A subjective belief in the existence of a risk, even one made in good faith, will not shield the decisionmaker from liability. Id. This Circuit has held that an employer must gather “substantial information” about an employee’s work history and medical status. Nunes, 164 F.3d at 1248 . The decision must be based upon “particularized facts using the best available objective evidence as required by the regulations.” Lowe v. Ala. Power Co., 244 F.3d 1305 , 1309 (11th Cir.2001); cf. McGregor v. Nat’l R.R. Passenger Corp., 187 F.3d 1113, 1116 (9th Cir.1999) (holding that policies requiring employees to be “100% healed” before returning to work violate the ADA because they preclude individualized assessment of whether employee can perform the essential functions of the job with or without accommodation).

Echazabal has raised a material issue of fact as to whether Chevron’s decision was “based on a reasonable medical judgment that relies on the most current medical knowledge and/or the best available objective evidence.” 29 C.F.R. § 1630.2 (r). As part of the physical examinations ordered by Chevron, Dr. Baily, and later Dr. McGill, administered and relied upon tests that measure the levels of three enzymes in the bloodstream. Based on results demonstrating abnormally high levels of certain enzymes, Drs. Baily and *1029 McGill concluded that Echazabal’s liver was not functioning properly, and recommended that Echazabal not be exposed to chemicals that could be toxic to his liver. 4 Neither Dr. Baily nor Dr. McGill has any special training in liver disease. Baily’s area of medical expertise is in preventive medicine, while McGill is a generalist, with no board certification in any specialty. In contrast, Echazabal’s experts, Dr. Fedoruk and Dr. Gitnick, are specialists in toxicology and liver disease. 5 Their opinions demonstrate that enzyme tests do not produce information regarding liver function. Rather, enzyme tests reflect only that an infection is ongoing. According to Fedo-ruk and Gitnick, the only tests that do measure liver function — blood albumin levels and prothrombin time — revealed that Echazabal’s liver was functioning properly. Far from showing “cutting edge research,” as Chevron argues, these opinions offered the unequivocal assessment that Echazabal could work at the refinery without facing a substantial risk of harm, beyond that faced by other workers. The required assessment could not be based upon “common sense,” as Chevron argues, but rather only after — at a minimum — a consultation with a medical professional who had made an “objective, scientific” judgment. Bragdon, 524 U.S. at 629 , 118 S.Ct. 2196 .

Echazabal presents evidence that there was no scientific basis for the contrary opinions of Chevron’s doctors. Both Dr. Gitnick and Dr. Fedoruk stated that “there is no medical or scientific evidence” supporting a finding that Echazabal’s chemical exposures from working as a plant helper or in the coker unit would present an appreciable or clinically significant risk. Dr. Fedoruk indicated that for some of the chemicals identified as potentially risky for Echazabal, an individual would receive a higher dosage from a daily multivitamin tablet than Echazabal would receive from working in the refinery. Based on the opinions of Drs. Fedoruk and Gitnick, a reasonable jury could conclude that Chevron failed to rely upon a “reasonable medical judgment that relies on the most current medical knowledge and/or on the best available objective evidence.”

In addition, the record does not support the district court’s conclusion that the medical opinion letters from Echazabal’s doctors evaluating his specific position all concurred that the job posed a “serious, immediate risk to him.” On April 5, 1993, Dr. Ha wrote: “In my opinion the patient is now capable of carrying on with the work that he has applied for and there is no restriction on his activity at work as outlined by the working condition sheet GO 308 that was sent to me.” 6 Dr. Ha stated that Echazabal’s prognosis “should be very good.” Dr. Ha’s opinion, based on her knowledge of Echazabal’s potential work environment, does not support the view that she concurred in Chevron’s assessment. 7 On November 10, 1993, and *1030 July 20,1994, Dr. Suchov wrote two letters indicating that there was “no limitation” on Echazabal’s ability to work and that he could return to his “usual duties.” Although the district court dismissed these letters because they did not address Echa-zabal’s specific job duties, Echazabal’s declaration states that he informed all of his doctors of the type of work that he performed. These letters, together with Echazabal’s own declaration, raise a material issue of fact as to the objective reasonableness of Chevron’s opinion.

The dissent describes as “clincher” the communications between Dr. McGill and Dr. Weingarten, one of Echazabal’s treating physicians, in which Dr. Weingarten recommended against exposure to hepato-toxic hydrocarbons. The sum total of the recommendation was as follows:

This general statement, which followed a statement that Echazabal was in good health and showed no sign of liver failure, is insufficient to carry Chevron’s burden of establishing that it relied on the “most current medical knowledge and/or the best available objective evidence” and that it considered the likelihood of harm, its possible severity, and imminence. Notably missing from this statement is any indication that Dr. Weingarten was asked to consider the specific chemical exposures, to indicate the levels at which they would • become dangerous or the likelihood that they would injure Echazabal, or even whether the risk to Echazabal was any greater than that for a healthy individual. (Indeed, it is difficult to imagine that any responsible doctor would recommend exposure of even his healthiest patient to an unspecified amount of hepatotoxic chemicals.) The district court notably found that “Dr. Weingarten was not informed by Dr. McGill about the specific chemicals to which plaintiff would be exposed, or the levels of concentration of those chemicals.”

Chevron was required to do more than consider generalized statements of potential harm. Before refusing to hire Echazabal, Chevron was required, under the terms of 29 C.F.R. § 1630.2 (r), to consider the severity, imminence, and potential likelihood of harm. Based on consideration of these factors, Chevron had the burden of demonstrating at least a “significant risk of substantial harm” to Echazabal. Id. The EEOC’s Interpretive Guidance for this section explains that where the employer invoking the direct threat defense relies on threats to the employee, the employer must determine that there is a “high probability of substantial harm” to the individual. 29 C.F.R. pt. 1630 App. (EEOC Interpretive Guidance on Title I of the ADA) (“Interpretive Guidance ”). Echazabal has raised a material question of fact as to whether Chevron made an adequate analysis. Dr. Weingarten’s general statement, unrelated to the demands and conditions of the particular position or the likelihood, imminence, or potential severity of harm (or even whether Echazabal was at greater risk than a healthy individual), would not preclude a reasonable juror from concluding that Chevron failed to make the required assessment.

*1031 2. Evaluation of the Arline factors

Had Chevron conducted the individualized assessment required by law, it would have considered in detail the four Arline factors as they applied to Echazabal’s condition. Chevron argues that there are no genuine issues of material fact with regard to the four Arline factors to be considered in assessing whether Echazabal’s condition posed a “direct threat.” While Echazabal concedes that the first Arline factor — the duration of his condition — is not disputed, he has raised material issues of fact about the three remaining factors.

First, Echazabal has raised a material issue of fact as to whether Chevron properly assessed the nature of the potential harm. The record indicates that the Chevron doctors were unfamiliar with the specific risks of Echazabal’s position. Dr. Baily stated in his deposition that he did not know the types or concentrations of toxin, liquid, or vapor exposures Echazabal would face in the coker unit, that he made no attempt to ascertain this information and did not contact either the Industrial Hygiene Department or an outside specialist to determine whether Echazabal could perform the plant helper job. He indicated that solvents are only liver toxic “in sufficient quantities,” but he made a blanket recommendation that all exposure be avoided. He made only a general recommendation that Echazabal not be exposed to hepatotoxins, unrelated to any specific position, assuming that it was management’s responsibility to determine Echaza-bal’s fitness for a particular job, and that he was not charged with considering specific exposure levels or chemicals. In fact, Dr. Baily anticipated that management would contact a specialist. He stated that the limitations “were not specifically based on any ... individual work place exposure. The limitations were placed in general fashion to give guidance to management so that they would then be able to work with the specialist in determining which jobs might be appropriate for that applicant or employee.”

Similarly, Dr. McGill testified in his deposition that, at the time he assessed Echazabal, he did not know the levels of hydrocarbons to which a plant helper would be exposed, was not aware if any regulatory levels would be exceeded, and that he did not attempt to contact the Industrial Hygience Department to determine whether the industrial setting in the coker unit would be harmful to Echazabal. 8 Although he contacted Industrial Hygiene with regard to other employees, Dr. McGill did not do so in Echazabal’s case because he assumed that it “had been thoroughly worked over in the 1992 phase [a]nd [he] was assuming that it had been investigated.” 9

*1032 Moreover, neither of the Chevron doctors had expertise in this area. Dr. Baily stated that he was not a liver specialist, that his experience with patients with chronic liver diseases was “very limited,” that he was “not familiar with the specific biochemistry of liver abnormalaties,” that he had not spoken with a liver specialist about Echazabal’s case, and that he was not aware of specific evidence that hepato-toxins pose a risk to individuals with hepatitis. Dr. Baily had no knowledge of whether Chevron ever contacted a specialist about the position. Similarly, Dr. McGill had not treated any patients in the prior 15 years for chronic liver disease, did not consult any treatises on the issue, did not research the likelihood of fiver failure due to exposure to fiver toxins, and did not consult a specialist.

According to Dr. Fedoruk, who did review Chevron’s records, the level of toxins present at the coker unit placed Echazabal at no greater risk of injury than other workers. He also stated that there was no reliable scientific or medical evidence to suggest that the other exposures would lead to hepatoxieity and most of the potential exposures identified by Chevron were insignificant. Dr. Gitnick opined that Echazabal was “at no greater risk of injuring himself and specifically his fiver than any other employee.” He stated that the contrary opinions of Chevron’s doctors were simply wrong and unsupported by medical evidence.

Second, the declarations of Fedoruk and Gitnick suggest that, at the time of Chevron’s evaluation, there was little indication that Echazabal faced potential harm that was (a) likely, or (b) imminent. For example, Dr. Gitnick stated that “I can say to a reasonable degree of medical certainty that Mr. Echazabal is in no greater risk of injuring himself and specifically his fiver by working in the refinery than other employee [sic]. His fiver is functioning properly and there is no evidence of liver failure.” Dr. Fedoruk also indicated that his tests had remained stable over years of work at the refinery. These statements were not, as Chevron implies, merely differences of medical opinion. In several instances, Fedoruk and Gitnick declared that Chevron doctors were simply wrong in their assessment of Echazabal’s condition and that their analysis is inconsistent with the literature on fiver function. The Chevron doctors, unlike Fedoruk and Git-nick, were not experts in this field.

Finally, this Circuit has cautioned that individualized risk assessment also requires consideration of relevant information about an employee’s past work history. See Nunes, 164 F.3d at 1248 ; Mantolete v. Bolger, 767 F.2d 1416, 1423 (9th Cir.1985) (holding that, in assessing elevated risk to an employee under the Rehabilitation Act, the employer- must “gather [and assess] all relevant information regarding the applicant’s work history and medical history”); see also Anderson v. Little League Baseball, Inc., 794 F.Supp. 342, 345 (D.Ariz.1992) (giving “great weight” to fact of disabled plaintiffs three years of service without incident in rejecting employer’s direct threat defense). Chevron gave no weight to the fact that Echazabal had worked at the El Segundo refinery, without incident or injury, for over 20 years. A reasonable jury could find that this injury-free work history provided evidence that Echazabal would not pose a direct threat to himself as a coker -unit employee. 10

*1033 3. Consideration of Echazabal’s medical experts’ opinions

Chevron argues that the opinions offered by Echazabal’s experts, Drs. Fedoruk and Gitnick, should not be considered because they were offered after the employment decision to exclude Echazabal from the refinery. Expert evidence of this nature, however, elucidates the very issue the court must assess — whether the opinion that a direct threat existed was objectively reasonable. See Bragdon, 524 U.S. at 649 , 118 S.Ct. 2196 ; Nunes, 164 F.3d at 1248 (analysis of direct threat “requires the employer to gather ‘substantial information’ about the employee’s work history and medical status, and disallows reliance on subjective evaluations by the employer”). The two expert opinions were directed in significant part to the state of medical knowledge — the best available objective evidence — at the time of Chevron’s employment action. At the very least, they were highly relevant to that question. The subjective belief of Chevron’s doctors is not relevant. Id.

Chevron also argues that to consult the Fedoruk and Gitnick opinions would be contrary to Cook v. United States Dep’t of Labor, 688 F.2d 669 (9th Cir.1982). Cook addressed a claim under the Comprehensive Employment and Training Act of 1973, and preceded Bragdon , as well as the 1990 enactment of the ADA and the 1991 issuance of the EEOC regulation. See Equal Employment Opportunity for Individuals With Disabilities, 56 Fed.Reg. 35734 (1991) (codified at 29 C.F.R. pt. 1630) (issuing regulations pursuant to the ADA and noting that the ADA was signed into law on July 26, 1990). Moreover, Cook did not involve the application of a regulatory requirement that the employer’s assessment be “based on a reasonable medical judgment that relies on the most current medical knowledge.” Thus, because of these differing circumstances, Cook is unhelpful, much less controlling, in determining whether an employer has complied with the EEOC’s ADA regulations requiring an individualized assessment based on the Arline factors and “the most current medical knowledge and/or the best available objective evidence.” As the Supreme Court emphasized, the requirement of an individualized assessment in 29 C.F.R. § 1630.2 (r) serves an important role in protecting against the risk of pater nalism the ADA was enacted to discourage. See Echazabal, 122 S.Ct. at 2052-53 .

Finally, we note that there is no medical evidence in the record.to support Chevron’s assertion that the opinions of Drs. Fedoruk and ’ Gitnick were not “available” to Chevron when it made its assessment. Neither is there a showing that the body of medical knowledge on which those opinions were based was not available at the time, i.e., was beyond the then “most current medical knowledge.” Given this medical knowledge, there is an issue of material fact whether the medical judgments which formed the basis of Chevron’s assessment were based on “the most, current medical knowledge and/or the best available objective evidence,” as required by the EEOC’s regulation. 29 C.F.R. § 1630.2 (r). 11

*1034 At the heart of Chevron’s arguments lies an unfounded fear that a proper application of the “individualized assessment” standard requires employer awareness of cutting-edge medical research not generally known to or accepted within the medical community. This is not the case. Chevron asserts that by relying primarily upon the advice of a generalist and an expert in preventive medicine in order to come to a conclusion about Echazabal’s liver problem, it met the statute’s requirements. Before terminating an individual’s livelihood, the ADA requires more.

The dissent contends that Chevron did enough. The dissent’s quibble, however, is less with our opinion and more with the requirements of the ADA. The dissent makes little mention of the rigorous requirements of § 1680.2(r) and the employer’s burden of proving that it complied with those requirements before it can rely on the direct threat defense. Rather, it states vaguely that Chevron’s decision was made “after appropriately and thoroughly considering all relevant factors,” that “the process [was not] defective or unreasonable,” that Chevron did not have to seek an outside expert in liver disease so long as, its decision was “objectively reasonable under the circumstances,” and it dismisses the Fedoruk and Gitnick opinions as irrelevant “to the bona fides and quality of Chevron’s decision.” None of these statements, however, expresses the governing standard for reviewing Chevron’s decision.

Were we reviewing an administrative agency’s decision under the substantial evidence standard of review and limited to the administrative record made before the agency, we might agree that the decision was not an abuse of discretion. That, however, is not our task on this appeal. Rather, without weighing the evidence at this summary judgment stage, we must *1035 decide only whether Echazabal has raised a material question of fact as to whether Chevron has met its burden under § 1630.2(r). 12 See Suzuki Motor Corp. v. Consumers Union of United States, Inc., 330 F.3d 1110 , 2003 WL 21137731 , at *18 (9th Cir.2003) (“it is not our role, at this stage, to take sides in this way”). He has succeeded in doing so.

B. Accommodation and the Interactive Process

Finally, Echazabal contends that Chevron failed adequately to address its duty to accommodate Echazabal and to initiate an interactive process prior to terminating his position. Echazabal, however, did not raise this issue in the district court in opposition to Chevron’s motion for summary judgment, and we decline to consider it here. See Bolker v. Comm’r, 760 F.2d 1039, 1042 (9th Cir.1985) (stating that, subject to limited exceptions, “we will not consider an issue raised for the first time on appeal”). Moreover, it is unnecessary to address this issue in the absence of an opportunity for the district court to address it, given that the grant of summary judgment must be reversed.

CONCLUSION

For the foregoing reasons, we conclude that disputed issues of material fact remain with respect to Chevron’s obligations under the EEOC’s direct threat regulation. We therefore reverse the district court’s summary judgment in favor of Chevron and remand for further proceedings consistent with this opinion and the Supreme Court’s opinion in Echazabal. 13

REVERSED and REMANDED.

. Given the short period of time between Echazabal’s physical and Chevron's withdrawal of its job offer, it is not surprising that Echazabal was unable to marshal expert medical opinion that he could work safely in the coker unit. The dissent’s criticism that Echa-zabal failed promptly to demonstrate his fitness for the position ignores both this short time frame and the manner in which Chevron’s decision was communicated to him.

Given this short time frame, it also appears unlikely that Chevron considered whether any *1027 measures could be taken to minimize the perceived risk to Echazabal. Dr. McGill, the Chevron doctor who considered Echazabal's case in 1996, testified that he did not contact the Industrial Hygiene Department to determine whether protective measures could prevent injury to Echazabal. Because, however, the district court did not develop the record on whether Chevron attempted to accommodate Echazabal's condition prior to withdrawing its offer and, if so, what steps were taken, as we conclude in Part B, infra, we cannot address the reasonable accommodation issue on this record. Because the record has not been developed, the dissent's conclusion that accommodation would cause Chevron undue hardship "as a matter of law” is groundless speculation.

. These factors were first articulated by the Supreme Court in Sch. Bd. of Nassau County v. Arline, 480 U.S. 273, 288 , 107 S.Ct. 1123 , 94 L.Ed.2d 307 (1987), and are commonly referred to as the “Arline factors.”

. Chevron’s argument that it did not rely upon stereotypes in assessing Echazabal’s condition is besides the point. While the ADA was passed, in part, to counter stereotypical assumptions about the disabled that result in discrimination, 42 U.S.C. § 12101 (a)(7), the mere fact that an employer avoids stereotypes does not satisfy its affirmative obligation to make an assessment based on "the most current medical knowledge and/or on the best available objective evidence."

. Dr. McGill replaced Dr. Baily in July 1993. Baily conferred with McGill about Echaza-bal's condition, and McGill concurred with Baily’s conclusions.

. Dr. Fedoruk is a board-certified physician in Occupational Medicine, Industrial Hygiene, and Toxicology. Dr. Gitnick is Chief of the Division of Digestive Diseases of the UCLA School of Medicine and a leading authority on liver disease.

. The GO-308 is Chevron's job summary for the coke handler and coke plant helper positions. It identifies airborne contaminants and chemicals in the work environment, including "hydrocarbon liquids and vapors, acid, caustic, refinery waste water and sludge, petroleum solvents, oils, greases [and] chlorine bleach.”

. The district court incorrectly states that this letter did not relate to the 1995 job offer and that there was no record evidence that the letter was seen by Chevron’s doctors or Ir *1030 win's expert, Dr. Tang. The job that Echaza-bal applied for in 1995 was a "plant helper” position at the coker unit described in GO 308, which was reviewed by Dr. Ha. In addition, Dr. Tang specifically references Dr. Ha's letter in his deposition when describing the contents of Echazabal's medical file. Dr. Ha’s letter was directed to Chevron and was part of Echazabal’s record.

. Dr. McGill's declaration states that he reviewed the job description for the plant helper position, which provided information that the position involved exposure to various chemicals, fumes, etc., and the same GO-308 that Dr. Ha reviewed. Thus, at least by the time he made his declaration, Dr. McGill may have had a general knowledge that some exposure would occur in the position.

. Thus, the dissent is incorrect in suggesting that the Chevron doctors based their determination on considerations of the specific risks of the position for which Echazabal applied. It states that Drs. Baily and McGill were "personally familiar with the conditions and demands of the work at issue,” and that Dr. McGill "determined that the chemicals and solvents to which Mr. Echazabal would be exposed at the refinery would further damage his reduced liver capacity and seriously endanger his health and his life.” In fact, neither doctor considered the risks of the specific position. As we have shown in the text above, Dr. Baily assumed that this would be done by management in conjunction with a specialist and Dr. McGill assumed that it had already been done.

. Chevron and the dissent emphasize the risk to Echazabal during an explosion or other emergency. There is no indication in the record, however, that Chevron considered the likelihood that this would occur and whether Echazabal was at any greater risk than other *1033 employees. Moreover, the Interpretive Guidance indicates that “generalized fears about risks to individuals with disabilities in the event of an evacuation or other emergency [cannot] be used by an employer to disqualify an individual with a disability.” 29 C.F.R. pt. 1630 App.

. The dissent mistakenly overstates the importance of a treating physician's opinion, both factually and legally. As a factual matter, Dr. Weingarten made only a general comment about exposure to hepatotoxins. He simply did not provide a recommendation relating to the specific risks of the position. At *1034 a minimum, his opinion should not be granted more weight than Dr. Ha’s earlier opinion that Echazabal had no work restrictions. As a legal matter, the dissent relies on cases from an unrelated context — the review of Social Security disability benefit determinations. Judicial review of such administrative decisions is governed by the substantial evidence rule. Tackett v. Apfel, 180 F.3d 1094, 1097 (9th Cir.1999). We grant substantial deference to the agency because "[i]f the evidence can reasonably support either affirming or reversing the [agency's] conclusion, the court may not substitute its judgment for that of the [agency].” Reddick v. Chater, 157 F.3d 715, 720-21 (9th Cir.1998). In contrast, in an action to enforce the ADA, the employer’s determination of unemployability is not entitled to any deference. Further, the judicial proceeding is not limited to the review of an “administrative” record, but the district court conducts plenary trial proceedings, as appropriate. While a treating physician’s opinion may be particularly relevant to the agency’s task of determining the extent of a disability in the Social Security context, there is no comparable requirement, as there is under § 1630.2(r), to consider the "most current medical knowledge and/or the best available objective evidence.” Cf. Black & Decker Disability Plan v. Nord, — U.S. -, 123 S.Ct. 1965 , 155 L.Ed.2d 1034 , 2003 WL 21210418 (U.S.2003) (rejecting the importation of the treating physician rule from the Social Security context to cases brought pursuant to ERISA, 29 U.S.C. § 1001 et seq.). Drs. Fedo-ruk and Gitnick opined that Chevron did not consider the correct tests of liver function and did not properly assess the level of risk in light of the most current medical knowledge. Their knowledge and assessment of the state of medical knowledge would not have been improved by treating Echazabal. The Interpretive Guidance does not place special emphasis on treating physicians, but rather indicates that their opinions, as well as those of experts on the disability in question, are relevant. 29 C.F.R. pt. 1630 App. ("Relevant evidence may include ... the opinions of medical doctors ... who have expertise in the disability involved and/or direct knowledge of the individual with the disability.”). The weight to be given the treating physician’s view will depend on all of the circumstances of the patient’s case, including the nature and extent of the care and the degree of knowledge the physician may have as to the physical dangers the particular work environment presents.

. The dissent acknowledges that the expert opinions of Drs. Fedoruk and Gitnick on the one hand, and Dr. Tang on the other, create a dispute as to whether Echazabal could safely work in the refinery. This is precisely the type of dispute which renders summary judgment inappropriate. While the dissent would like us to discount the Fedoruk and Gitnick opinions because they were not presented to Chevron earlier, it relies heavily on the Tang opinion, which was also not before Chevron. In fact, all of these opinions are relevant to the quality of Chevron’s decision-making. We also decline the dissent’s offer to count up the doctors giving negative assessments because we do not weigh the evidence at the summary judgment stage.

. The parties agree that the same standards apply under the ADA, the Rehabilitation Act of 1973, and the parallel state law, the California Fair Employment and Housing Act, on the "direct threat” issue. Accordingly, in our prior opinion, we vacated the district court’s grant of summary judgment with respect to those other claims as well. 226 F.3d at 1072 n. 12. We also reversed the district court’s judgment on the claim for punitive damages. Id. Given our reversal of the grant of summary judgment on the ADA claim, we reiterate these dispositions.