Postiive end-expiratory pressure (PEEP), in combination with mechanical ventilation, is efficacious in the treatment of some forms of adult respiratory insufficiency. PEEP in excess of 10 to 15 torr usually is not recommended; however, higher levels of PEEP may be required to reverse the pulmonary venous admixture. The efficacy of optimizing cardiopulmonary function with varying levels of PEEP is described.