Thermodynamic properties of poly(vinylpyrrolidone) (PVP) were studied by laser-light-scattering, membrane osmometry, and isopiestic measurements. Four polymer samples of weight-average molecular mass between about 9000 and 1 200 000 were investigated at temperatures from (278 to 333) K. The experimental results are described with application of the osmotic virial equation and compared to literature data.