This study examined the effects of ozone (O3) inhalation on mucociliary clearance from the tracheobronchial tree. Rabbits were exposed for 2 h at 0.1, 0.25, and 0.6 ppm or for 2 h/d for 14 consecutive days at 0.25 and 0.6 ppm. Clearance was assessed by measuring the retention of radioactivity tagged, inert tracer particles inhaled immediately after the single 2-h exposure, or 24 h after 2, 7, or 14 of the daily exposures. Single exposures resulted in a concentration-related trend toward retarded particle clearance, with a statistically significant difference occurring after exposure to 0.6 ppm. Intermittent exposures produced no significant change in clearance rate, although there was a suggestion of retarded clearance at early time points at both 0.25 and 0.6 ppm.