In situ photon transmission experiments were performed using an ultra-violet-visible (u.v.-vis) spectrometer during the multiple swelling of polyacrylamide (PAAm) gel in water. The transmitted light intensity, I, decreased continuously as the PAAm gel swelled. The decrease in I, was attributed to the increase in scattered light intensity which might have orginated from the contrast between 'frozen blob clusters' and holes in the swollen gel. It was observed that the correlation length, xi(c), increased by 1/4 power of the swelling time. The sudden increase in the gel relaxation time, tau, was attributed to the rupture of the network structure after the eighth swelling step during multiple swelling of the PAAm gel. (C) 1998 Elsevier Science Ltd. All rights reserved.