Hydrogels with varying cross-linking densities, and average molecular weights between two consecutive cross-links, were prepared from the binary poly(N-vinyl-2-pyrrohdone)/water and ternary poly(N-vinyl-2-pyrrolidone)/water/K2S2O8 systems by irradiation withy gamma-rays at ambient temperature. Both hydrogel systems were employed for diffusion and swelling experiments in 0.00278 M alpha-lactose solution at room temperature. Diffusion of alpha-lactose solution into hydrogels was found to be of the Fickian type. The percent swelling, equilibrium swelling, initial rate of swelling, swelling rate of constant, equilibrium water/alpha-lactose content, and diffusion constant values were determined for PVP and PVP/K2S2O8 hydrogel systems in 0.00278 M alpha-lactose solution. (C) 2003 Wiley Periodicals, Inc.