This paper focuses on the determination of the swelling pressure of polymeric hydrogels by variation of the composition of the monomer mixture used for synthesis via free radical polymerization. The method used is based on the principle of determining the swelling pressure at a given final volume of swelling. Data for different types of low swollen hydrogels based on weakly crosslinked poly(acrylic acid)/poly-(sodium acrylate) copolymers are presented for swelling in deionised water. For polymer volume fractions phi(P) between 0.03 and 0.30, swelling pressures p in the range of 0.20-4.23 MPa were obtained. No effect on the swelling pressure could be found by variation of monomer concentration and crosslinker content. In contrast, the content of sodium acrylate had an effect on the swelling pressure. The results are discussed based on the effect of counterion condensation. (C) 2009 Elsevier Ltd. All rights reserved.