Summary Human alveolar macrophages were collected postmortem and their granules were analyzed for acid phosphatase, beta-glucuronidase and elastase-like esteroprotease. Alveolar macrophages from BCG-vaccinated rabbits were also studied. The alveolar macrophage granule preparations showed satisfactory levels of acid hydrolases but were nevertheless low in elastase-like esteroprotease activity when compared to human polymorphonuclear leukocyte granules. Part of the reduction in enzyme may be accounted for by differences in lysosomal content of the granule preparations from these two cell types. Human alveolar macrophage granules showed elastinolytic activity commensurate with their esterolytic activity against t-BOC-l-alanine p-nitrophenol. The macrophage alanine-p-nitrophenyl esterase was not affected by an endogenous inhibitor of the leukocyte esterase. The possible role of these enzymes in the pathogenesis of emphysema remains to be explored.