The clinical and physiologic effects of bronchopulmonary lavage of both lungs at separate times in 14 patients with alveolar proteinosis proved by biopsy were followed for 2 to 96 months. Before lavage, all patients had moderate to severe dyspnea on exertion. Twelve had a nonproductive cough, and 2 had a productive cough; both were smokers. Nine had generalized fatigue, and 4 had weight loss. Twelve of 14 had fine inspiratory rales. All of the patients had abnormal chest roentgenograms, and 13 of 14 had an increased lactate dehydrogenase concentration. After lavage, all patients had loss of fatigue and improved exercise tolerance, with most returning to normal activity. Cough cleared in 12 of 14 and remained only in the cigarette smokers. Inspiratory rales cleared completely in most patients (11 of 12) and partially in one. The rales usually returned during exacerbations. Physiologic measurements that changed significantly after bilateral lavage included: vital capacity, total lung capacity, resting room air PO2, exercise PO2, PO2 while breathing 100 per cent O2, and DLCO. Because all measurements were made within 5 days of the second lavage, one must attribute the acute improvement to the removal of proteinaceous material from the alveoli. The long-term effects varied; some patients required annual or semiannual lavages, wherease others remained in remission after lavage for 36 to 96 months. Exacerbations were accompanied by increased dyspnea, reappearance of rales, and deterioration of the gas-exchange parameters noted previously. Repeat lavage reversed the clinical symptoms and physiologic abnormalities in patients who had recurrences.