The aqueous equilibrium swelling properties of a series of lightly-cross-linked cationic hydrogels based on acrylamide and [(methacrylamido)propyl]trimethylammonium chloride (MAPTAC) were measured as a function of initial total monomer concentration %T (w/v) and ionic strength. Swelling is a strong decreasing function of rising %T; the 10%T hydrogel obtained a 17-fold larger swelling ratio (g of swollen hydrogel/g of dry hydrogel) in pure water compared to the 40%T hydrogel. Good agreement is obtained between measured swelling equilibria in aqueous sodium chloride and that calculated from a Flory-type swelling model including ideal Donnan equilibria provided that an adjustable parameter is introduced into the swelling model for hydrogels in pure water. The experimental results presented here indicate that network-chain interpenetration increases with rising %T.