The whole three-electrode cell set-up electrical equivalent circuit, EEC, involving parasitic stray impedance is applied in the analysis of impedance spectra of thin polyaniline, PANI, film modified working electrodes in conditions of gradually reduced films and changes of the solution resistance term. It is shown that the frequency region of parasitic stray impedance response is determined by two characteristic time constants of three-electrode cell. The values of time constants are determined by total stray capacity and total stray inductivity of the cell and solution resistance formed between the working and reference electrodes. A type of frequency response of parasitic stray impedance (almost capacitive or almost inductive) is determined by the higher time constant. Extent of influence of parasitic stray impedance on the recorded impedance spectra is determined by impedance of the working electrode and solution resistance. Neglect of contribution of parasitic stray impedance to impedance spectra, particularly of low and moderately high electrode impedance(s) such as PANI film modified electrode in conducting and partially reduced state(s) in electrolyte solutions of high(er) conductivity, will always result in rather uncertain values of the evaluated model parameters. (C) 2009 Elsevier B.V. All rights reserved.