Partial venovenous cardiopulmonary bypass with a membrane oxygenator was used to exchange respiratory gases during and after bilateral lung lavage in a patient with severe hypoxemia caused by pulmonary alveolar proteinosis. The patient was unable to tolerate an attempt at lung lavage without bypass. Therefore, extracorporeal perfusion safely supported the patient's respiration for 32 hours, buying time to lavage each lung separately and to enable sufficient recovery of transpulmonary gas exchanging capacity.