Increasingly, physicians are encountering difficulties in differentiating between impairment of health due to insidious exposure to chemicals and disease caused by other etiological factors. This situation is emphasized by the vast number of new chemicals being introduced every year into industry and everyday life. It has been our experience that painstaking scrutiny of all available data can materially increase diagnostic accuracy in such cases. We have applied principles of critical interpretation of laboratory data and physical findings. Even more so, we have analyzed the importance of accurate determination by the physician of the factual environmental exposure, not only in quantitative terms of the alleged offender, but also in respect to concomitant exposure both on and off the job.