Poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate) p(HEMA-GMA) membrane was prepared by UV-initiated photopolymerisation of 2-hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) in the presence of an initiator, azobisisobutyronitrile (AIBN). Cholesterol oxidase was immobilised directly on the membrane by forming covalent bonds between its amino groups and the epoxide groups of the membrane. An average of 53 mug of enzyme was immobilised per cm(2) of membrane, and the bound enzyme retained about 67% of its initial activity. Immobilisation improved the pH stability of the enzyme as well as its temperature stability. The optimum temperature was 5degreesC higher than that of the free enzyme and was significantly broader. The thermal inactivation rate constants for free and immobilised preparations at 70degreesC were calculated as k(i (free)) 1.06 x 10(-1) min(-1) and k(i (imm)) 2.68 x 10(-2) min(-1), respectively. The immobilised enzyme activity was found to be quite stable in the repeated experiments. (C) 2002 Society of Chemical Industry.