Invertase and amyloglucosidase were entrapped in polyvinyl alcohol membranes through UV irradiation of pendent styrylpyridinium groups. The influence of cross-linking on immobilization efficiency was studied using prepolymers with varied cross-linker density, the above mentioned enzymes of different molecular weight, and various substrates. It was found that the larger enzyme invertase is effectively immobilized even in polymers with very low contents of the cross-linking component. In contrast for an effective immobilization of amyloglucosidase, a higher degree of cross-linking is necessary. Although there is only a slight loss in amyloglucosidase activity the apparent activity, especially for the macromolecular substrate starch, is low. This is contributed to a hindered diffusion of the substrates in the swollen hydrogel matrix. The influence of the diffusion is also reflected in the kinetic parameters K-m and V-max The pH and temperature optima of entrapped amyloglucosidase are similar to those of the native enzyme in solution.