Human urinary trypsin inhibitor (UTI) and (4-(2-carboxyethyl) phenyl trans 4-aminoethylcyclohexanecarboxylate hydrochloride (DV-1006) competitively inhibited the human acrosomal proteinase acrosin; Ki values were 1.2 x 10-8 M and 9.4 x 10-7, respectively.