Gels are crosslinked macromolecules (polymer networks). The crosslinking results in an elastic behavior of the polymer network. When the segments of the network contain hydrophilic groups, the gels are called "hydrogels". Hydrogels respond to their surroundings by a volume change, i.e. they swell or shrink. This paper reports new experimental results for the swelling behavior of some nonionic, synthetic hydrogels of N-isopropyl acrylamide in aqueous solutions of a single organic solvent (acetic acid and pyridine) at 298 K. The experimental results are correlated applying a thermodynamic model, which combines an expression for the Gibbs energy of a liquid phase with an equation for the Helmholtz energy of an elastic network. (c) 2005 Elsevier B.V. All rights reserved.