Hydrogels containing tetraprotic acid moieties sensitive to pH changes of the swelling medium were prepared from the ternary systems acrylamide/ethylene diamine tetraacetic acid/water by irradiation with gamma-rays at ambient temperature. Gel compositions of poly(acrylamide-g-ethylene diamine tetraacetic acid) [P(AAm-g-EDTA)] hydrogels were determined by using a differential pulse polarography technique. Equilibrium swelling behaviour of these hydrogels was studied using an equation, based on the Flory-Huggins thermodynamic theory, the phantom network theory of James-Guth, and the approaches of Brannon-Peppas and Peppas, which was modified by the authors for determination of M-c and chi parameters. The equation modified by the authors for the determination of M-c and chi parameters were observed to describe very well the swelling behaviour of the charged polymeric network. (C) 2003 Wiley Periodicals, Inc.