To investigate whether intersubject variations in the dose of inhaled ozone (O3) cause corresponding variations in the physiological response, 28 female and 32 male nonsmokers participated in a 1-h continuous inhalation of clean air or 0.25 ppm O3 while exercising on a cycle ergometer at a constant ventilation rate of 30 L/min. The exposure protocols included continuous monitoring of respiratory flow rate and O3 concentration from which O3 uptake (OZU) and fractional uptake efficiency (UE) were computed. Pre-to-post changes in forced expired volume in 1 s (%ΔFEV 1), peripheral cross section for carbon dioxide diffusion (%ΔAP), and Fowler dead space volume (VD) were also measured for each exposure. Individual values of UE ranged from .70 to .98 among all the subjects, with significant differences (p<.05) existing between men and women. These intersubject differences were inversely correlated with breathing frequency and directly correlated with tidal volume. The mean ± SD values of %ΔFEV1, %ΔAP, and %ΔV D were all significantly more negative in the O3 exposure session (-13.31 ± 13.40, -8.14 ± 7.62, and -4.20 ± 5.12, respectively) than in the air exposure session (-0.06 ± 4.56, 0.22 ± 10.82, and -0.70 ± 6.88, respectively). Finally, our results showed that neither %ΔFEV1 nor %ΔVD was correlated OZU, whereas there was a significant relationship (ρ = -0.325, p = .0257) between %ΔAP and OZU. We conclude that the overall uptake of O3 is a weak predictor of intersubject variations in distal airspace response, but is not a predictor of intersubject variations in conducting airway responses.