We compared the tracheal mucus clearance rate (TMCR) in anesthetized dogs during spontaneous breathing (SB), ventilation by high-frequency oscillation at the airway opening (HFO/AO), and ventilation by high-frequency oscillation of the chest wall (HFO/CW). The HFO/AO was carried out by using a piston pump with a high impedance transverse flow at the proximal end of the endotracheal tube; HFO/CW was effected by creating rapid pressure oscillations in an air-filled cuff wrapped around the lower thorax of the animal, causing small tidal volumes at the mouth. The TMCR was measured by observing the rate of displacement of a charcoal marker in the lower trachea; a fiberoptic bronchoscope was used to deposit the marker before each experiment and to relocate it after a 5-min run. In 7 dogs, mean TMCR during control (SB) was 8.9 +/- 3.5 mm/min. At 13 Hz with an oscillatory tidal volume (VTO) of 1.5 ml/kg, mean TMCR was 240% of control with HFO/CW (p less than 0.001) and 76% of control with HFO/AO (NS). During HFO/AO at 20 Hz and a VTO of 3 ml/kg, mean TMCR was 97% of control. We conclude that high-frequency ventilation by rapid chest wall compression enhances tracheal mucus clearance when compared with spontaneous breathing, whereas high-frequency oscillation at the mouth does not.