Five enzyme inhibitors (phenylmethylsulfonyl fluoride, 4-amidinophenylmethanesulfonyl fluoride, 4-(2-aminoethyl)benzenesulfonyl fluoride, Nor-p-tosyl-L-lysine chloromethyl ketone, and N-tosyl-L-phenylalanine chloromethyl ketone) in buffer, DMSO, or stock solutions were completely degraded by adding 1M NaOH and the final reaction mixtures were not mutagenic. The stability of these compounds decreased as the pH increased.