Hydrogels were prepared by gamma-ray-induced polymerization in aqueous solution of N-isopropylacrylamide (NIPA) and of NIPA with three different charge densities, that is, maleic acid (MA) as a comonomer. The swelling behaviors of these hydrogels were analyzed in buffer solutions at various pH and temperature ranges. The equilibrium swelling ratios were relatively high and sensitive to pH and temperature. The polymer-solvent interaction parameter (chi) and the molecular weight between crosslinks ((M) over bar (c)) of P(NIPA/MA) polyelectrolyte hydrogels were calculated from swelling studies in buffer solutions at various pH values and related to MA content. A kinetic study of the absorption determined the transport mechanism as a non-Fickian type diffusion. (C) 2004 Wiley Periodicals, Inc.