Barley beta-amlyase was immobilized on two polymeric materials; poly(acrylamide-acrylic acid) resin [P(AM-AAc)] and poly(acrylamide-acrylic acid-diallylamine-HCl) resin [P(P(AM-AAc-DAA-HCl) using two different methods: covalent and cross-linking immobilization. Thionyl chloride, used to activate the polymers for covalent immobilization, has the advantage that it is able to react with a number of surface groups of protein under very mild conditions. Cross-linking with glutaraldehyde gave a higher coupling yield (approximately 70%) than covalent immobilization (approximately 20%). The activity and stability of the resulting biopolymers have been compared with those of free beta-amylase. The specific activity of the immobilized enzyme was significantly influenced by the amount of enzyme loaded onto the polymers, the optimal level being 3.5 mg g(-1) polymer. It was found that the immobilized beta-amylase stored at VC retained approximately 90% of its original activity after 30 days, whereas free beta-amylase stored in solution at 4degreesC retained only 47% of its activity after same period. The difference in long term stability was more significant when the enzyme was stored at room temperature; the immobilized enzyme maintained 40% of its activity after 30 days, whereas the residual activity of free enzyme was only 10%. (C) 2003 Society of Chemical Industry.