Disk shaped poly acrylamide (PAAm) gels were prepared from acrylamide (AAm) with Various N,N'-methylenebis(acrylamide) (Bis) contents by free radical crosslinking copolymerization (FCC) in water and dried before use in swelling experiments. Photon transmission experiments for these gels were performed using an UV-visible (UW) spectrometer. Transmitted light intensity, I,from the gel increased at very early times when the PAAm gels are immersed in water, then decreased exponentially as the swelling time increased. Decrease in I,was attributed to the lattice heterogeneities which might be originated between "frozen blob clusters" and holes in the swelling gel. Decrease in I, was modeled using the Li-Tanaka equation from which cooperative diffusion coefficients, D-c were determined for various Bis content gels. It is observed that the D-c values increased as the Bis content increased. (C) 2000 Elsevier Science Ltd. All rights reserved.