We have studied the lipid composition and protein content of 99 pulmonary washings from patients with asthma, chronic bronchitis, pulmonary adenomatosis, desquamative interstitial pneumonia, and pulmonary alveolar proteinosis. Phospholipid represented 31.1% to 47.0% of recovered lipid in patients with asthma and bronchitis. Patients with alveolar proteinosis had the highest lipid (mean value 129.4 mg/100 ml effluent) of which 56% was phospholipid. One patient with pulmonary adenomatosis had 42.4% phospholipid and one with desquamative interstitial pneumonia had 26%. Palmitic acid comprised 78% of the total fatty acids of phosphatidylcholine obtained from patients with alveolar proteinosis but only 62% in others. Repeated lung washings in alveolar proteinosis patients showed progressive decrease in lipid and protein concentration. Lipid and protein composition of human lung washings tends to reflect the nature of the underlying disease.