To test the effect of the matrix polymer on diffusion, we have measured the self-diffusion coefficients of water and poly(ethylene glycol) of a molecular weight of 600 (PEG-600) in aqueous systems of selected polymers using the pulsed-gradient spin-echo NMR technique. The polymers used in this study include poly(vinyl alcohol) (PVA), hydroxypropyl methyl cellulose (HPMC), poly(N,N-diethylacrylamide) (PNNDEA), and poly(N-isopropylacrylamide) (PNIPA). The polymer concentrations varied from 0 to 0.38 g/mL. The effect of the polymer network on the self-diffusion coefficients of the solvent (water) and a solute (PEG-600) was investigated by analyzing the diffusion data with the use of the free volume model of Yasuda et al. [Yasuda, H.; Lamaze, C. E.; Ikenberry, L. D. Makromol. Chem. 1968, 118, 19], the diffusion model proposed by Phillies [Phillies, G. D. J. Macromolecules 1986, 19, 2367], and the model of Petit et al. [Petit, J.-M.; Roux, B.; Zhu, X. X.; Macdonald, P. M. Macromolecules 1996, 29, 6031]. The results obtained with PVA, HPMC, PNNDEA, and PNIPA are used to evaluate the applicability of these models in polymer-water-solute ternary systems. The physical significance of the parameters used in the models is discussed.