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Several types of PHEMA membranes were prepared via photopolymerization. In some applications, glucose oxidase (GOD) was entrapped in the bulk of the membrane or between layers. In others it was covalently bonded on the membranes. The effect of chemical composition and various initiators on the entrapped GOD were determined. In the entrapment in the bulk it was found that as the monomer concentration in the polymerization medium increased, the GOD activity decreased. Among the initiators used, the highest enzyme activity was obtained with AIBN (71 % ). Efficiency of immobilized enzyme activity was found to be 98.5 %, 93.7 % for entrapment, (in the bulk and between layers) and 17.4 % for covalent bonding. A significant effect of the method used was observed on the stability of the enzyme upon use or storage. Although dependent on the operation mode (continuous or repeated use) and substrate concentration as well as on the entrapment method, activity retention to a level of 90% after 6 h continuous operation was possible. The water contents of PHEMA membranes increased with ionic strength and decreased with the ionic radii of the ions in preparation medium. The highest permeability (36.1OxlO-8cm2.s-1) was obtained with the membrane containing GOD entrapped in the bulk.