The acyl transfer of phenylalanine to MeOH by means of chymotrypsin starting from phenylalanine Pr ester has been studied. This transesterification turns out to be useful for producing optically pure phenylalanine esters as well as for the optical resoln. of phenylalanine. The L-phenylalanine Me ester may be obtained with yields >80%. The reaction medium required for transesterification represents a special case with respect to the use of org. solvents in enzymic catalysis, since MeOH can be regarded as a water miscible org. solvent, but behaves, in addn., as a cosubstrate. [on SciFinder (R)]