alpha-Chymotrypsin was covalently attached to an alpha-alumina ultrafiltration membrane coated with an inert protein. This derivative was used as catalyst for the continuous kinetically controlled synthesis of kyotorphin in both membrane and packed bed reactors, using aqueous (water/dimethyl sulfoxide, 60:40, v/v) and nearly-dry (hexane/ethanol/water, 57:40:3, by vol.) organic media, respectively. In both media, the synthetic activity and operational stability of the enzyme-membrane derivative was compared with an adsorbed alpha-chymotrypsin Celite derivative, being 2-times and 4-times respectively, higher than the Celite one. The enzyme-membrane derivative showed half-life times higher than 36 days, with a selectivity near to 100%.