In this study, phenylalanine as a hydrophobic ligand was covalently attached on a comonomer, methacryloyl chloride. Then, poly(2-hydroxyethyl methacrylate-co-methacrylamido-phenylalanine), poly(HEMA/MAPA), membranes were prepared by UV-initiated photopolymerization of 2-hydroxyethyl methacrylate and methacrylamido-phenylalanine. The lipase adsorption of these poly(HEMA/MAPA) membranes was determined by changing the hydrophobic ligand density, pH, temperature and concentration of lipase in the adsorption medium. The lipase adsorption capacity of the membranes increased as the ligand density on the membrane surface increased. The nonspecific adsorption of lipase on the poly(2-hydroxyethyl methacrylate) membranes was negligible (12 mug cm(-2) of membrane). The adsorption phenomena appeared to follow a typical Langmuir isotherm. The maximum adsorption capacity (Q(m)) of the poly(HEMA/MAPA-5) membrane for lipase was 215 mug cm(-2) of membrane. The equilibrium constant (k(d)) value was 1.43mg ml(-1). The lipase could repeatedly be adsorbed and desorbed on the affinity membrane without any significant loss in the adsorption capacity of the membrane. (C) 2002 Society of Chemical Industry.