Two different active membranes were prepared by simple (membrane M1) or mixed-entrapping (membrane M2) covalent attachment of alpha -chymotrypsin onto an alpha -alumina tubular support coated with an inert protein. The derivatives were used as catalyst for the continuous kinetically controlled synthesis of kyotorphin in organic media. Contrary to adsorption, the covalent linkage of the enzyme to a dynamic membrane allows a continuous peptide synthesis and enhances operational stability towards the denaturative effects of organic solvents.