AbstractThe effect of polydispersity on estimates of molecular parameters (statistical segment length, molecular mass per unit contour length and chain thickness) was investigated using viscosity and sedimentation data on polymers with stiff chains. Theoretical functions of Yamakawa and Fujii for a monodisperse polymer and correction functions for polydispersity were used. The effect is very strong in the treatment of sedimentation data, while in the treatment of viscosity data it is still tolerable.