A new method for the assay of peptidase activities is developed based on the oxidative deamination of L-amino acids with L-amino acid oxidase. This method measures the products of the enzymatic hydrolysis, without any interfrence from the peptides. Brush border membrane hydrolvzes very rapidly tri- and tetra-L-alanine, L-lencyl-glycyl glycine, L-leucyl-glycine, L-phenylalanyl-L-alanine, and L-leucine amide. The enzymatic activities of the brush border membrane hydrolyzing L-phenylalayl-L-alanine and L-leucine amide were characterized with regard to pH-activity curves, ion activation, and intracellular distribution. The results suggest that intrinsic enzymes of the brush border membrane play a role in the teminal digestion of proteins.