Acute exposure of humans to ozone is known to acutely cause pulmonary function decrements, inflammation, and increased permeability of pulmonary epithelium. Fifteen healthy male and female nonsmoking subjects were exposed, on different occasions, to clean air and 0.4 ppm ozone for 1 hour while they exercised continuously. Pulmonary function was measured immediately before and after exposure and 90 min and 24 hours after exposure. Each subject returned the next day for a final particle retention measurement. Despite significant changes in pulmonary function, there was no difference in mean whole lung retention time of particles between clean air and ozone exposures, indicating that mucociliary transport is unaffected by ozone exposure when it is measured 2 hours after exposure.