L-Phenylalanine was produced from phenylalanine Pr esters by chymotrypsin in 2-phase systems (org. phase using iso-Bu Me ketone and aq. phase). Control of pH during the enzymic reaction was crit. The reaction was carried out in a batch fermentor or a fixed-bed reactor. It was also possible to use chymotrypsin immobilized in 3-aminopropyltriethoxysilane and(or) glutaraldehyde-activated silica gel. [on SciFinder (R)]