The fraction of an inspired chlorine (Cl₂) bolus absorbed during a single breath (Λ) was measured as a function of bolus penetration (V_P) into the respiratory system of five male and five female nonsmokers during both nasal and oral breathing at a quiet respiratory flow of 250 ml/s. The correspondence between V_P and specific anatomic landmarks was found for each subject by a combination of acoustic reflection and nitrogen washout measurements. For both nasal and oral breathing, Λ reached ∼0.95 at the distal end of the upper airways and reached 1.00 within the lower conducting airways. The values of a regional mass transfer parameter computed from the Λ-V_P data indicated that the resistance to Cl₂ diffusion in the airway mucosa was negligible compared with the diffusion resistance in the respired gas. Changing the peak inhaled Cl₂ concentration from 0.5 to 3.0 parts/million did not significantly affect the distribution of Cl₂ absorption, suggesting that the underlying mass transport and chemical reaction processes were linear with respect to Cl₂concentration.