duration of enhanced responsiveness upon reexposure to ozone it has been repeatedly observed that ozone o3 reexposure within 24 h elicits enhanced pulmonary function responses however there are only limited observations concerning reexposure to o3 at intervals between 24 h and several days the present study was designed to assess the effects of reexposure to 035 ppm o3 at intervals of 24 48 72 and 120 h forty young adult male subjects were assigned randomly to one of four groups in ascending order of time to reexposure groups 14 each exercised on a bicycle ergometer for 60 min at a workload that elicited a mean ventilation of 60 lmin on three occasions protocol 1 p1 filtered air fa protocol 2 p2 035 ppm o3 and protocol 3 p3 035 ppm o3 in addition to standard pulmonary function measures specific airway resistance sraw exercise ventilatory pattern ie respiratory frequency fr and tidal volume vt and subjective symptoms ss were assessed statistical analysis revealed significant differences p less than 05 for all groups between the fa p1 responses and those for the two o3 exposures p2 p3 for forced vital capacity fvc forced expiratory volume in 1 s fev10 sraw fr vt and ss when the two o3 exposures p2 and p3 were compared only group 1 24 h responses were statistically significant upon reexposure fev10 161 vs 304 p less than 003 sraw 205 vs 345 p less than 05 fr 442 vs 653 p less than 001 and ss p less than 015abstract truncated at 250 words