Suctioning of the tracheobronchial tree during high frequency jet ventilation (HFJV) in two groups of apneic dogs could be prolonged to 2 min without producing significant drops in PaO2, slowing of the pulse or marked hypertension. Arrhythmias were also virtually absent. The controls reacted to suctioning like human patients. A sharp drop in PaO2, an increase in PaCO2 and a change in pulse rate and blood pressure (BP) as well as frequent premature ventricular contractions were observed.