A patient with sarcoma, pleural effusion, fever, and tachypnea was intubated and mechanically ventilated. After stabilization, exploratory surgery discovered a retroperitoneal abscess, which was drained. Left-sided tension pneumothorax occurred two days postoperatively and was successfully treated by a chest tube. Pulmonary status deteriorated and a persistent left-sided air leak developed at airway pressures above 35 cm H₂O, while adequate ventilation was impossible at lower pressures. To ventilate the patient in the presence of the bronchopleural fistula, a Carlens double-lumen endobronchial tube was inserted and two separate MA-1 ventilators were used to inflate the right and left lungs with different tidal volumes and PEEP. Ventilator cycling was controlled with a Healthdyne IMV controller. Differential ventilation with PEEP continued four days; the P(A - a)02 decreased, the air leak was abolished, and chest tube suction was discontinued. Complications involving a possible brain abscess led to the patient's death on the 34th hospital day. Use of a double-lumen endobronchial tube and differential lung ventilation prevents the collapse of the diseased lung that occurs if a bronchopleural fistula is treated by endobronchial intubation and ventilation of the normal lung. It is important to fix the double-lumen tube in position; this can be done by wiring it to the upper teeth and supporting the portion of the tube outside the mouth by suspension.