The issues surrounding diagnosis of an environmental medical disorder, as well as a method for diagnosis of such an illness by a physician, were discussed. The concerns of the patient, the physician, and the agendas of third parties such as lawyers and employers were explored in relation to the diagnosis of an environmental medical condition. The clinical approach was broken down into four steps. Step one was establishing the clinical characteristics of the medical condition, which involves establishing a pathophysiological basis for disease, preceding establishment of cause. This can be performed through determination of the involved organ system, taking of medical history, and ordering of laboratory tests. Step two involved characterizing exposure; methods for determining exposure were discussed, including patient interviews, use of company, government and community records, and visiting the exposure site. Four cardinal exposure indices were laid out: material agent; duration of exposure; magnitude of exposure; relationship between exposure and clinical manifestation. Step three was demonstrating a correlation between exposure and clinical manifestation through the use of exposure assessment, epidemiological and toxicologic data bases, use of clinical studies and case reports, clinical experience, objective evidence of overexposure, the effects of removal from and reexposure to the agent, exploring preexisting illness, multiple causes of illness, temporal relationship of exposure and illness, clinical evaluation of dose response and variation in susceptibility. The fourth step was establishing the diagnosis of an environmental medical condition by the use of information garnered in steps one through three; also, through semiquantitative estimation of alternative possibilities, a diagnosis can be established. The authors note that diagnosis is part science and part art; the physician must use a scientific approach to diagnosis while using his individual judgment.