Hydrogels with varying cross-linking densities and average molecular weights between two consecutive cross-links were prepared from the binary poly(N-vinyl-2-pyrrolidone)/water and ternary poly(N-vinyl-2-pyrrolidone)/water/ K2S2O8 systems by irradiation with gamma rays at ambient temperature. Both hydrogel systems were employed for diffusion and swelling experiments in 0.1 g/100 ml Bovine Serum Albumin (BSA) solution at room temperature. Diffusion of BSA solution into hydrogels has been found to be of the Fickian type. The percent swelling, equilibrium swelling, initial rate of swelling, swelling rate of constant, equilibrium water/BSA content, and diffusion constant values were evaluated for PVP and PVP/K2S2O8 hydrogel systems at 0.1 g/100 ml BSA solution. (C) 2004 Elsevier Ltd. All rights reserved.