Diffusivities of aqueous dilute and semidilute polyvinylpyrrolidone solutions M(w)=50,500 and M(w)=867,000 were measured at 25 degrees C. The measurements were performed by Taylor’s hydrodynamic stability method and the dynamic light scattering (DLS) method. Taylor’s method was compared to DLS and evaluated as an experimental technique to determine the molecular diffusivity in polymer solutions. The agreement between the two methods was very good with Taylor’s method proving to be a reliable, simple, and inexpensive technique that provided diffusivity data with a maximum error of 5%.