Measurements are reported of the swelling pressure omega and of the collective diffusion coefficient D-c in two series of salt-free neutralized polyelectrolyte gels, one a poly(acrylamide-acrylic acid) copolymer, the other cross-linked potassium polyacrylic acid. The values of D-c measured by macroscopic deswelling are in reasonable agreement with those measured by dynamic light scattering. D-c increases as the degree of swelling of the gel increases, with similar behaviour being found for the elastic modulus G. The osmotic pressure, II= omega + G, displays a power law behaviour over the concentration range explored, the exponent sigma depending on the counter-ion concentration: sigma approximate to 1 for the sample of lower charge density, while for the sample with a high charge density, sigma approximate to 1.5. The latter behaviour, unexpected at low polymer concentrations, is interpreted in terms of the inequivalence between static and dynamic concentration fluctuations.