A new explanation of the asymmetry and large anodic residual current in the cyclic voltammograms for redox reactions of poly(3-methylthiophene) is proposed on the basis of voltammetric measurements for films of different thicknesses. A specially designed measurement procedure shows that the anodic branch is a superposition of two overlapping oxidation peaks. The less positive peak is ascribed to oxidation of long-chain polymer segments which are formed mainly at the beginning of the electropolymerisation. The more positive peak originates from oxidation of short-chain segments which mainly contribute to the polymerisation of thick films. Thick poly(3-MeT) films, with polymerisation charges larger than 12 mC cm(-2), are a mixture of the long- and short-chain segments due to participation of oligomers in the extended polymerisation process. The thin films are better-ordered and more compact than the thicker ones. The change in morphology of the poly(3-MeT) films is confirmed by the scan rate dependence of currents of both anodic peaks and by the UV-VIS absorption spectra of the films.