Bronchoalveolar lavage was performed in 28 patients with pulmonary sarcoidosis. Enzyme cytochemical staining with the tartrate-resistant acid phosphatase revealed a significantly increased portion of sarcoidosis macrophages showing a monocyte-like phenotype. Immunocytochemical staining with the proliferation-associated monoclonal antibody Ki-67 showed an increase of proliferating monocyte/macrophages related to disease activity in sarcoidosis. A functional activation of alveolar macrophages in sarcoidosis is indicated by spontaneous interleukin-1 secretion and increased release of oxygen free radical in sarcoidosis alveolar macrophages.