Hydrogels in the form of rods with varying crosslink densities and three-dimensional network structures were prepared from Poly(N-vinyl-2-pyrrolidone) (PVP)/water and PVP/water/persulfate systems by irradiation with gamma rays at ambient temperature. Average molecular weights between crosslinks, percent swelling, swelling equilibrium values, diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant), and equilibrium water content were evaluated for both hydrogel systems. Water diffusion to the hydrogel is a non-Fickian type diffusion and diffusion coefficients vary from 6.56 x 10(-7) to 2.51 x 10(-7) cm(2)min(-1) for PVP and 6.09 x 10(-7) to 2.14 x 10(-7) cm(2)min(-1) for PVP/persulfate hydrogel systems.