In this study, a hydrophobic group containing monomer, 2-methacrylamidophenyalanine (MAPA) was prepared by using methacrylochloride and phenylalanine. Then, poly(2-hydroxyethyl methacrylate-co-methacrylamido-phenlyalanine) (pHEMA-MAPA) membranes were prepared by UV-initiated photopolymerization of HEMA and MAPA in the presence of an initiator alpha-alpha'-azobisisobutyronitrile (AIBN). The lipase was immobilized onto these membranes by covalent bonding through carbodiimide activation. The amount of enzyme loading on the membranes was increased as the MAPA ratio increased in the membrane structure. Immobilization improved the pH stability of the enzyme as well as its temperature stability. Thermal stability was found to increase with immobilization and at 60 degreesC the thermal stability constants were 1.1 x 10(-1) min for free enzyme and 1.2 x 10(-2) min for the immobilized enzyme. The immobilized enzyme activity was found to be quite stable in repeated experiments. (C) 2002 Elsevier Science Ltd. All rights reserved.