Tracheal (Ptr) and esophageal (Pes) pressure and flow were measured in 12 supine anesthetized paralyzed normal subjects aged 16–22 yr. The subjects were ventilated with a fixed inflation volume (range 0.57–0.62 liter) and with different constant flows ranging between 0.24 and 1.12 l/s. A rapid airway shutter (closing time 10–15 ms) was used to briefly occlude (0.4–0.9) the airways at end inspiration for 33–44 consecutive breaths. At each flow level, Ptr and Pes records obtained during end-inspiratory occlusions were ensemble averaged to allow for the cardiac artifacts. The interrupter resistances of the chest wall and respiratory system were assessed as the rapid fall in Pes and Ptr with occlusion divided by the flow preceding the occlusion. Interrupter resistances of both the chest wall and lung were independent of flow and averaged 0.4 +/- 0.1 and 1.5 +/- 0.4 (SD) cmH2O.s.l–1, respectively. The contribution of the chest wall to the total interrupter resistance was approximately 27% at flows < or = 1 l/s.