Highly swollen hydrogels in the rod form were prepared by copolymerization of acrylamide and crotonic acid with gamma-radiation. The swelling took place in water at 25 degrees C and was followed by weighing. The influence of dose and relative content of crotonic acid on the swelling properties, diffusional behavior of water, diffusion coefficients, and network properties of hydrogel systems were examined. Acrylamide-crotonic acid hydrogels were swelled in the range 900-2300%, while polyacrylamide hydrogels swelled in the range 650-700%. Water diffusion to the hydrogels was of non-Fickian type diffusion.