A highly purified (237-fold) preparation of extracellular Leu-Gly-Gly aminopeptidase was isolated from the 716 strain of mould Aspergillis flavus. The enzyme was found electrophoretically and enzymatically homogeneous, using Leu-beta-naphthylimide as substrate. The pH optimum is 8.60; the temperature optimum is about 50 degrees C. The enzyme was inhibited by EDTA and completely reactivated by Co2+ ions; Ca2+ and Mn2+ ions considerably restored the enzyme activity. The enzyme showed the optimal activity during the cleavage of substrates, containing N-terminal leucine. Mild hydrolysis of leucine-free tripeptides and dipeptides with N-terminal glycine and alanine was observed. The enzyme was found to be stereospecific in some respects. Peptides with a blocked terminal NH2-group are not hydrolyzed by the enzyme.