The concept of distributed formal redox. potentials is employed to analyse and study the i/E response of different arylamine-derived polymers, poly-o-aminophenol (POAP), poly-o-phenylenediamine (POPD) and polybenzidine (PBZ), and a conducting polymer, poly-o-toluidine (POT), in different electrolytic media. The analysis of the experimental data allows determining the formal redox. potential distribution. The experimental formal redox potential distributions are interpreted on the basis of a simple statistical thermodynamic model that considers the possibility of expansions and contractions during the oxidation-reduction cycles applied to the polymer. It is considered that units having several redox centres constitute the polymers and that these units change in size during the oxidation-reduction cycles. The analysis of the experimental formal redox potential distribution allows obtaining the number of redox centres per polymer unit, the ratio of the internal partition function of the units and the formal redox potential of the centres. These results are in agreement with the previous studies on the electrochemical behaviour of these polymers.