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A stereospecific enzyme activity capable of cleaving the amide bond of the synthetic substrate N-benzoyl-D-arginine-p-nitroanilide (D-BAPA) has been found in all aerobic and anaerobic members of the family Bacillaceae tested by us. Cells of nonsporeforming gram-positive or gram-negative bacteria contain a hydrolase activity stereospecific to N-benzoyl-L-arginine-p-nitroanilide. The D-BAPA-hydrolyzing enzymes (D-BAPAases) of mid-logarithmic-phase cells of Bacillus subtilis 168 and B. cereus T were compared. These enzymes had the same molecular weight of approximately 66,000 in gel filtration and the same electrophoretic mobility after electrophoresis on polyacrylamide gels. The D-BAPAases of B. subtilis 168 and B. cereus T differed in the effect of inhibitors on enzymatic activity. While both hydrolases were inhibited by tosyl-L-lysine chloromethyl ketone and tosyl-L-arginine-methyl ester as well as leupeptin, only the D-BAPAase of B. cereus T was inhibited by p-chloromercuribenzene sulfonic acid. The D-BAPAases of B. subtilis and B. cereus T had a Michaelis constant for D-BAPA of 2.9 x 10(-5) M and 1.4 x 10(-4) M, respectively. D-BAPAase is an intracellular enzyme localized in the protoplast (80 to 90% in soluble form in the cytoplasm). The ability to cleave D-BAPA is suggested as an additional chemotaxonomic characteristic of sporeforming bacteria of the genera Bacillus and Clostridium.