The interaction between bleomycin (BLM) and angiotensin-converting enzyme (ACE) from bovine lungs, serum, and cultured pulmonary artery endothelial cells was examined. ACE activity from all sources was inhibited by metal-free BLM but not by metal-complexed BLM. The metal-free deamide metabolite of BLM, which is nontoxic, also inhibited ACE activity from bovine endothelial cell homogenates and serum. Incubation of intact cultured pulmonary artery endothelial cells for 1 h with metal-free BLM produced a concentration-dependent inhibition of cellular ACE activity, which was persistent, lasting at least 24 h after drug removal. In addition, the enzyme activity released into the culture medium was decreased. The inhibition of cellular ACE activity occurred in the absence of (1) cell death as measured by dye exclusion, (2) inhibition of total protein synthesis as measured by [3H]leucine incorporation, and (3) decreased cellular enzyme content as assayed using a monoclonal antibody against the enzyme. These results indicate that a brief exposure of intact cultured pulmonary endothelial cells to BLM can produce direct and prolonged inhibition of ACE activity. The inhibition of ACE activity does not relate directly to cell death but rather appears to result from metal chelation by BLM.