A method suitable for assaying chymotrypsin in crude biological materials such as feces has been described. The procedure employs a water soluble peptide, N-benzoyl- l-tyrosyl-para-aminobenzoate (Na), which is hydrolyzed by chymotrypsin ( K m = 2.9 × 10 −3 M) to yield the TCA-soluble diazotizable aromatic amine.