The bacterial phosphotriesterase has been shown to be capable of catalyzing the hydrolysis of a P-S bond in organophosphate triesters. The V-max values for the hydrolysis of the insecticides, acephate (O, S-dimethyl N-acetylphosphoramidothioate) and methamidophos (O, S-dimethyl phosphoramidothioate) are 140 and 6 min(-1), respectively. The (Sp)-enantiomers are hydrolyzed at a rate that is 100-fold faster than the (Rp)-enantiomers.