An l-aminopeptidase of Pseudomonas putida, used in an industrial process for the hydrolysis of d,l-amino acid amide racemates, was purified to homogeneity. The highly l-enantioselective enzyme resembled thiol reagent-sensitive alkaline serine proteinases and was strongly activated by divalent cations. It possessed a high substrate specificity for dipeptides and alpha-H amino acid amides, e.g., l-phenylglycine amide.