Recent evidence suggests that prolonged exposures of exercising men to 0.08 ppm ozone (O3) result in significant decrements in lung function, induction of respiratory symptoms, and increases in nonspecific airway reactivity. The purpose of the study was to confirm or refute these findings by exposing 38 healthy young men to 0.08 ppm (O3) for 6.6 h. During exposure, subjects performed exercise for a total of 5 h, which required a minute ventilation of 40 l/min. Significant (O3)-induced decrements were observed for forced vital capacity (FVC, -0.25 1), forced expiratory volume in 1 s (FEV(sub 1.0), -0.35 l), and mean expiratory flow rate between 25% and 75% of FVC (FEF(sub 25-75), -0.57 l/s), and significant increases were observed in airway reactivity (35%), specific airway resistance (0.77 cm H2O/s), and respiratory symptoms. These results essentially confirm previous findings. A large range in individual responses was noted (e.g., percentage change in FEV(sub 1.0): 4% increase to 38% decrease). Responses also appeared to be nonlinear in time under these experimental conditions.