Homogenous human angiotensin converting enzyme (EC 3.4.15.1) cleaves dipeptides from the C-terminus of substrates containing a free carboxyl group. In this study we demonstrate that peptides containing a C-terminal nitrobenzylamine are also cleaved by the enzyme. The hydrolysis of these substrates is inhibited by the specific converting enzyme inhibitors captopril and MK421 as well as by anti-converting enzyme antibody. Sodium chloride accelerates the rate of hydrolysis forty-fold. The product of the reaction, an amino acid nitrobenzylamide, was identified by thin layer chromatography and high performance liquid chromatography. These results suggest that the carboxyl group is not an absolute requirement for substrate hydrolysis.