Six normal subjects, two of whom were heavy smokers, underwent broncho-alveolar and bronchial washings. The aim of our work was to compare the biochemical composition of these fluids. Quantitative measurements of total protein, IgG AND IgA were made, the percentage of IgA 7S among the IgA population was established, an immunoelectrophoretic study was carried out, and glycosidase and protease activities were determined. In a given subject, the bronchial washing always showed more IgA, 11S and more concentrated glycosidase activities than the broncho-alveolar washing; the latter had higher values for IgG and protease activities, the most important being chymotrypsin-like activity. In both fluids, IgA 11S represented the main part of IgA population.