Some intracellular enzyme-activities of BCG-activated alveolar macrophages (AM) and peritoneal macrophages (PM) were studied. It was found that (in normal) the activities of acid phosphatas (ACP), succinate dehydrogenase (SDH), non-specific esterase (NSE) in AM were higher than those in PM, but that of lactate dehydrogenase (LDH) was lower. Both in BCG activated AM and PM, the activities of ACP, SDH, NSE increased significantly, and that of LDH also enhanced in activated AM but not in PM.