ONODERA, T., NAKAMURA, M., SATO, T. and AKINO, T. Biochemical Characterization of Pulmonary Washings of Patients with Alveolar Proteinosis, Interstitial Pneumonitis and Alveolar Cell Carcinoma. Tohoku J. exp. Med., 1983, 139 (3), 245-263 -We have studied the biochemical compositions of fifteen pulmonary washings from seven patients with alveolar proteinosis, and two washings from two patients with interstitial pneumonitis and two from two patients with alveolar cell carcinoma. The pulmonary washing was separated into the supernatant and precipitate fractions by a brief centrifugation. Analytical results revealed that the pulmonary washings from patients with alveolar proteinosis contained much more protein and lipids as well as a higher percentage of phospholipid than did the pulmonary washings from other patients. With regards to alveolar proteinosis, the precipitate fraction, i.e., water-insoluble material, contained lipids as the major component, the majority of which was dipalmitoyl phosphatidylcholine. Protein in the sedimental material was small in amount, but was composed of proteins mainly of molecular weights of 62, 000, 36, 000, 28, 000 and 15, 000 as measured by SDS-gel electrophoresis. On the other hand, the supernatant fraction, i.e., water-soluble material, was composed predominantly of serum proteins, with the lipid content being lower than those in the precipitate fraction. These analytical findings support the idea that materials normally existing in the alveoli are excessively accumulated as alveolar-filling materials in alveolar proteinosis. It was also noted that there were marked differences in the lipid profiles between pulmonary washings from patients with alveolar proteinosis, and those from patients with other diseases, indicating that the biochemical composition of pulmonary washings tends to reflect the nature of an underlying disease. From these findings, the cause of the alveolar-filling materials found in alveolar proteinosis was discussed.