The bolus inhalation method was used to measure the fraction of inhaled chlorine (Cl₂) and ozone (O₃) absorbed during a single breath as a function of longitudinal position in the respiratory system of 10 healthy nonsmokers during oral and nasal breathing at respired flows of 150, 250, and 1,000 ml/s. At all experimental conditions, <5% of inspired Cl₂ penetrated beyond the upper airways and none reached the respiratory air spaces. On the other hand, larger penetrations of O₃ beyond the upper airways occurred as flow increased and during nasal than during oral breathing. In the extreme case of oral breathing at 1,000 ml/s, 35% of inhaled O₃ penetrated beyond the upper airways and ∼10% reached the respiratory air spaces. Mass transfer theory indicated that the diffusion resistance of the tissue phase was negligible for Cl₂ but important for O₃. The gas phase resistances were the same for Cl₂ and O₃ and were directly correlated with the volume of the nose and mouth during nasal and oral breathing, respectively.