The linear extrapolation of (eta-eta(0))/(eta(0)c) towards c -> 0 constitutes the basis of traditional methods to determine intrinsic viscosities [eta], where eta is the viscosity of polymer solutions of concentration c and eta(0) is the viscosity of the pure solvent. With uncharged macromolecules this procedure works well; for polyelectrolytes it fails because of the pronounced non-linearity of the above dependence at high dilution resulting from the increasing electrostatic interactions. This contribution presents a new method for the determination of [eta]. It rests upon the application of the laws of phenomenological thermodynamics to the viscosity of polymer solutions and introduces a generalized intrinsic viscosity enabling a comparison of differently charged and uncharged polymers.