The HERL conducts a variety of investigations of the health effects of air pollutants to serve as criteria for the reevaluation of National Ambient Air Quality Standards. Human clinical studies include research on the effects of: (1) ozone (O3) and nitrogen dioxide (NO2) on exercising healthy adults, asthmatics, males vs. females, and blacks vs. whites; (2) O3 and NO2 on pulmonary cell biology and immunology; (3) carbon monoxide (CO) on cardiovascular physiology of patients with ischemic heart disease; and (4) CO on neurophysiology. Human research also includes investigation of the mechanisms of the effects of O3 and NO2 and the relationship between rate of exposure to CO and the level of carboxyhemoglobin formation and effects. The neurophysiological effects of lead are being investigated in humans and monkeys. Animal studies with O3 and NO2 include: (1) evaluation of the progression of chronic lung disease during chronic exposure, (2) determination of the effects on antiviral lung diseases, and (3) investigation of the mechanisms of effects. Quantitative animal-to-man extrapolation models for O3 and NO2 focused on dosimetry and species sensitivity, are under development.