The ac and electrohydrodynamical (EHD) impedances have been calculated for an electrode modified by a redox polymer in contact with a solution containing a redox couple. The expressions obtained are functions of the diffusion coefficient of electrons in the film, the redox capacitance of the polymer film and its thickness, and the faradaic impedances on both sides of the film. These impedances, established for a rotating disc electrode by considering quantitatively convective diffusion effects, were simulated to illustrate the relative contribution of each process.