Several abnormalities of alveolar macrophage function were found in patients with sarcoidosis, and such abnormalities reflected the recruitment of immature macrophages to the local sites. In this study, alveolar macrophage function was compared with the disease activity in patients with sarcoidosis. The alveolar macrophage phagocytic index correlated closely with the spleen index obtained by ultrasonography, but not with serum angiotensin converting enzyme levels, lung function tests, or the cell differentiations of bronchoalveolar lavage fluid. The patients who had a positive uptake of 67-gallium scintigram showed a higher phagocytic index and a higher percentage of CD15-positive alveolar macrophages than those with negative scintigrams. Acid phosphatase activity and the percentage of CD15-positive alveolar macrophages were increased in patients with negative PPD skin tests compared to those with positive tests. We previously reported that alveolar lymphocytes in patients with sacroidosis are sensitized to Propionibacterium acnes (P. acnes), which may play a significant role in the induction of alveolitis in these patients. There was a significant correlation between the blastogenesis of alveolar lymphocytes induced by P. acnes and beta-galactosidase activity as well as the percentage of CD14-positive alveolar macrophages. These findings suggest that alveolar macrophages play an important role in the pathogenesis of sarcoidosis, in which the clinical abnormalities may reflect abnormal alveolar macrophage function.