Catalase was entrapped in thermally reversible poly (isopropylacrylamide-co-hydroxyethyl-methacrylate) (pNIPAM/HEMA) copolymer hydrogels. The thermoresponsive hydrogels, in cylindIl-rical geometry, were prepared in an aqueous buffer by redox polymerization. It was observed that upon entrapment, the activity retention of catalase was decreased between 47 and 14%, and that increasing the catalase loading of hydrogel adversely affected the activity. The kinetic behaviour of the entrapped enzyme was investigated in a batch reactor. The apparent kinetic constant of the entrapped enzyme was determined by the application of lMichaeiis-Menten model and indicated that the overall reaction rate was controlled by the substrate diffusion rate through the hydrogel matrix. Due to the thermoresponsive character of the hydrogel matrix, the maximum activity was achieved at 25 degrees C with the immobilized enzyme. The K-m value for immobilized catalase (28.6mM) was higher than that of free enzyme (16.5mM). Optimum pH was the same for both free and immobilized enzyme. Operational, thermal and storage stabilities of the enzyme were found to increase with immobilization. (C) 1999 Society of Chemical Industry.