Cell lysates from cultured human alveolar macrophages contain detectable amounts of an elastinolytic enzyme. Although particulate elastin was solubilized only after prolonged incubations, lysates readily hydrolyzed T-OC-alanyl-p-nitrophenol-ester. Hydrolysis of the latter substrate was inhibited by the leukocyte elastase site-specific inhibitor, N-ac-(ala)4-chloromethyl ketone. In addition, radioimmunoelectrophoresis of concentrated alveolar macrophage lysates, previously incubated with 3H diisopropyl-phosphofluoridate (DFP), revealed the presence of DFP binding material that comigrated with inactivated human leukocyte elastase. Human leukocyte elastase can cause lung lesions resembling pulmonary emphysema in experimental animals; therefore, the clearance of this enzyme by alveolar macrophages may represent a significant route for the removal of this potentially pathogenic enzyme from the lung.