Well-defined and characterized polymeric matrices showing close chemical similarities but wide differences in water uptake and swellability in aqueous medium were used for lipase immobilization. Biphasic networks of 2-hydroxypropylcellulose (HPC) were synthesized with acrylamide (AAm), methacrylamide (MAAm), N-isopropylacrylamide (N-i-PAAm), and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and simultaneously crosslinked with N,N-methylene bisacrylamide in aqueous medium by using simultaneous gamma-radiation technique. Lipase enzyme was produced from a mesophilic bacterial isolate (HBK-8) and was immobilized onto all the matrices by adsorption method. The activity of the immobilized enzyme was optimized for pH, temperature, and amount of crude enzyme and effect of dehydration. High relative activity for the immobilized enzymes was observed and loss of activity with time was minimal; reusability was found to be good. The activity of the immobilized enzyme was also observed to be good in both esterification and hydrolysis of esters. In the present study, lipase immobilization, hydrolysis of p-nitrophenyl palmitate, and optimum pH and temperature for substrate hydrolysis were evaluated for different matrices to study polymer structure and enzyme activity relationship in diverse physical environments. (C) 2004 Wiley Periodicals, Inc.