Samples of a polyelectrolyte poly(methacryloylethyl trimethylammonium methylsulfate), PMETMMS, with molar masses M-w = 22-25 x 10(6) were examined with viscosity, static light scattering, and conductivity measurements in a water-acetone solvent. Because acetone is a nonsolvent for this polymer the measurements were performed to determine the influence of the solvent composition, the polymer concentration, and the presence of added ions on the conformation of the polyelectrolyte in mixed solvents. The possible influence of a hydrodynamic field on the polymer conformation was also studied. The viscosity of the polymer solutions as a function of polymer concentration, as well as of the solvent composition, was studied using a broad range of shear rates. When the mass fraction of acetone in the solvent, gamma, is below 0.5, the solutions show a usual polyelectrolyte behavior. When gamma greater than or equal to 0.80, the polymer adopts a compact conformation. This is observed as a decrease of the radius of gyration, R-g, second virial coefficient, Az, the viscosity, and also as a change in the conductivity of the solution. The change in the polymer conformation may be induced also by dilution. When 0.60 less than or equal to gamma < 0.80, a gradual decrease in the polymer concentration leads to a sudden decrease of the reduced viscosity, which indicates a decrease in the particle size. The values of M-w measured by static light scattering were constant in all experiments.