Alveolar macrophages from patients with active pulmonary sarcoidosis have been shown to secrete several factors, such as interleukin-1 and alveolar macrophage-derived growth factor. We examined alveolar macrophages from nonsmoking patients with sarcoidosis undergoing bronchoalveolar lavage (BAL) for evaluation of disease activity. We compared these cells with macrophages from smoking and nonsmoking control patients. The amount of hydrogen peroxide released by the macrophages either spontaneously or after stimulation by phorbol myristate acetate was measured. The alveolar macrophages from smokers spontaneously released hydrogen peroxide, as we previously observed. The macrophages from the patients with sarcoidosis also released detectable amounts of hydrogen peroxide, but the macrophages from the non-smokers did not. Alveolar macrophages from all three groups released hydrogen peroxide when stimulated with phorbol myristate acetate. The macrophages from all three groups were examined for the presence on the surface membrane of beta-galactosidase, an enzyme that appears on the surface of older, activated macrophages. The macrophages in the BAL fluid of the patients with sarcoidosis had less beta-galactosidase staining than did those from the smokers, although they released comparable amounts of hydrogen peroxide. These findings suggest that alveolar macrophages in the BAL fluid of patients with sarcoidosis are younger, more monocyte-like, and activated by various factors, including gamma-interferon.