Viscosity and density studies for 0.01-0.14% (w/w) poly(N-vinyl-2-pyrrolidone) (PVP) in water and in water and 0.01% bovine serum albumin (BSA) were conducted at 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15 K. The viscosity coefficients and the activation-energy, free-energy, enthalpy, and entropy changes were calculated from viscosity data for viscous flow. On this basis, PVP-PVP, PVP-BSA, PVP-water, and BSA-water interactions and PVP and BSA shape factors were investigated and rationalized in terms of the water structure.