A new mode, high-frequency alternating lung ventilation (HFALV) is described and demonstrated in which the lungs are alternately pulsed. A fluidic oscillator may be used to deliver two pulsed gas streams, 180 degrees out of phase, to bronchial catheters placed via a double lumen endobronchial tube. Inspiratory phase of one lung thus coincides with expiratory phase in the other, and characteristic lateral rocking chest movements is observed. In six dogs, HFALV was compared to simultaneous pulsing of both lungs with comparable flow (18.5 l/min), frequency (144 min-1), and pulse wave shape. Arterial PCO2 was significantly lower (P less than 0.001) with HFALV. Arterial PCO2 was also found to increase linearly (r = -0.862, P less than 0.001) with distance of the catheters' distal tips from the dogs' carinae. Theoretical mechanisms and possible applications of HFALV are discussed.