Methods for the preparation of p-amidinophenyl esters from amino acid derivatives are described. Blocking of the amidino function with the benzyloxycarbonyl group and its deblocking by catalytic hydrogenation after coupling were satisfactory. p-Amidinophenyl esters are of special interest because of their susceptibility to the hydrolytic enzyme, trypsin, and some parameters of the hydrolysis of these compounds by trypsin are presented.