The authors studied the abnormalities of gas exchange and lung mechanics in a canine model of bronchopleural fistula during intermittent positive pressure ventilation (IPPV) and high-frequency oscillatory ventilation (HFOV). The left lower lobe bronchus was opened to atmosphere and it was determined that end expired volume was best maintained at frequencies of 45–50 breaths/min. during IPPV. Comparing alternating periods of IPPV and HFOV in six dogs (Group 1) at matched airway opening pressure (Pao), we found that PaO2decreased significantly to 68 ± 14 mmHg and 69 ± 24 mmHg, respectively, on opening the fistula. In a second group of six dogs (Group 2), when Paowas increased by additional bias flow into the ventilatory circuit during both IPPV and HFOV, PaO2increased significantly to 89 ± 12 mmHg and 87 ± 8 mmHg, respectively. Repeating Group 2 studies after induction of oleic acid lowpressure pulmonary edema demonstrated that conventional IPPV was associated with large intrapulmonary shunts. HFOV, however, maintained gas exchange at near baseline values. For both Group 1 and Group 2, the calculated gas flow through the fistula was significantly less at all levels of airway pressure during HFOV. The authors conclude that HFOV offers advantages over conventional IPPV in the maintenance of oxygenation and in the reduction of gas leak through the fistula.