The continuous alpha-chymotrypsin-catalyzed peptide synthesis of kyotorphin, tyrosyl-arginine, via the N(alpha) formyltyrosyl-arginine propyl ester is described. For continuous process development, two reaction systems were studied: immobilized alpha-chymotrypsin covalently bound to Eupergit C packed in a column, and soluble alpha-chymotrypsin utilizing an enzyme membrane reactor. Selectivities and kinetic parameters are discussed. The use of soluble enzyme in an enzyme membrane reactor proved superior to the covalently immobilized enzyme. A significant loss of enzyme activity and a certain decrease of selectivity was observed during immobilization. It was shown that the addition of organic solvent, in this case n-propanol, causes a severe diminuation of the enzyme activity.