Studies of crude extracts of pea seeds (Pisum sativum, var. Green feast) revealed the presence of three enzymes that hydrolyse the amide bond of aminoacyl β-naphthylamides. They differ in their specificity towards the aminoacyl moiety; one is proline-specific, whereas the other two hydrolyse the β-naphthylamides of primary amino acids. Of the latter, one is highly specific for hydrophobic aminoacyl residues whereas the other has a broader, somewhat complementary specificity, showing preferential hydrolysis of non-hydrophobic aminoacyl residues. These latter two aminoacyl-β-naphthylamidases have been separated and partly characterized with regard to substrate specificity and antagonism by inhibitors. Both are true aminopeptidases, requiring the presence of a free amino group and hydrolysing the amide bonds of amino acid amides, dipeptides and oligopeptides consecutively from the N-terminal end.