The pulmonary function of 8 men and 8 women (51 to 76 years of age), all nonsmokers, was measured before and after 2-h exposures to filtered air (FA) and 0.45 ppm ozone (O 3). The subjects alternated 20-min periods of rest and 20-min periods of cycle ergometer exercise at a workload predetermined to elicit a ventilatory minute ventilation ( dot V E ) of approximately 25 L/min (BTPS). Functional residual capacity (FRC) was determined pre- and post-exposure. Forced vital capacity (FVC) was determined before and after exposure, and 5 min after each exercise period. Ventilatory minute volume ( dot V E ) was measured during the last 2 min of each exercise period, and heart rate was monitored throughout each exposure. The pulmonary function data were evaluated as the percentage change from pre- to post-exposure to partially remove the effect of differences between men and women in absolute lung volume. There were no statistically significant ( p > 0.05) differences between the responses of men and women to FA or O 3 exposure. There were no significant ( p > 0.05) changes in any variable consequent to FA exposure. Exposure to O 3 induced significant ( p > 0.01) decrements in FVC, FEV 3.0, and FEV 3.0 at post-exposure compared to pre-exposure. Ozone exposure induced no significant ( p > 0.05) effect on FEF25–75% or FEF75%. Men had a significantly ( p > 0.05) higher mean exercise V dot E than women (27.9 ± 0.29 L vs. 25.4 ± 0.8 L; mean ± SD. Since men and women had similar decrements in pulmonary function, even though the women inhaled less O 3, the data suggest that women may be somewhat more responsive to O 3 than men. We also compared the responses of our older subjects with those of young men and women that we studied with the same protocol, and with published results of other investigators who have studied young men and women. This comparison suggests that older individuals may be less responsive to O 3 than young individuals.