The activity of beta-galactosidase immobilized into a poly(2-hydroxyethyl methacrylate) (pHEMA) membrane increased from 1.5 to 10.8 U/g pHEMA upon increase in enzyme loading. The K-m values for the free and the entrapped enzyme were found to be 0.26 and 0.81 mM, respectively. The optimum reaction temperatures for the free and the entrapped beta-galactosidase were both found to be 50 degrees C. Similarly, the optimum reaction pH was 7.5 for both the free and the entrapped enzyme. The immobilized beta-galactosidase was characterized in a continuous system during lactose hydrolysis and the operational inactivation rate constant (k(iop)) of the entrapped enzyme was found to be 3.1 x 10(-5) min(-1).