The effect of monomer and electrolyte (LiCF3SO3) concentrations on the nucleation and growth processes of polythiophene, poly(3-methythiophene) and poly(3-hexylthiophene) electrogenerated on a platinum electrode in an acetonitrile media were studied. The current transients were fitted using a mathematical equation that considers up to seven contributions, each of them representing a different classical nucleation and growth mechanism. The results indicate that the electrogeneration of polythiophene and poly(3-methylthiophene) films follow a similar mechanism, two-dimensional processes being detected at short reaction times, the overall processes being governed at longer reaction time by an instantaneous three-dimensional nucleation under charge control mechanism. The electrogeneration of poly(3-hexylthiophene) films, however, takes place without overlapping of nuclei, the process now being governed by an instantaneous nucleation three-dimensional diffusion control mechanism. (C) 2001 Elsevier Science Ltd. All rights reserved.