In order to explain the impedance spectra of polymer film electrodes a modification of the porous model is suggested based on experimental observations. In this 'brush' model it is assumed that a polymer film consists of short and long polymer chains forming bundles in such a way that only a small part of the metal substrate is covered by the polymeric material. The oxide layer formation on the gold substrate attests the reality of this physical model. The model has been tested by the analysis of the impedance spectra of Au/poly(o-phenylenediamine) electrodes in contact with 1 mol dm(-3) perchloric acid. The spectra were taken at different potentials and the film thicknesses as well as the roughness of the gold substrate were systematically varied.