Effects of pH on the cyclic voltammetry of KI at high concentrations was studied at Pt and polyaniline-modified Pt electrodes. The mechanism of oxidation of iodide to iodine was almost identical at both bare and polyaniline-filmed Pt electrodes at pH less than or equal to 2. In cyclic voltammograms the redox peak currents increased, or new peaks occurred at polyaniline-filmed Pt electrodes, depending on the experimental conditions. The latter finding is due to the interactions of iodine species with the polyaniline main chains. At pH 4.7, the PAn film became electroinactive, the redox process proceeded at the Pt/PAn interface of the electrode. A change in the pH dependence of this kind was observed at a Pt electrode filmed with PAn modified by the presence of paraphenylenediamine in the growth solution.