The initial stage of silver electrocrystallization is studied at polyaniline (PANI)-coated platinum electrodes by means of potentiostatic current transients and electron microscopic observations. Data for the nucleation frequency and the number of active sites for nucleation are obtained by interpreting of current transients according to the theory for nucleation and 3D growth under diffusion limitations. It is found that depending on the PANI layers thickness, d, two different regimes for silver nucleation and growth exist. For thin PANI coatings (d < 0.3 mum), the crystallization occurs with high nucleation frequency at active sites located at the polymer layer/metal electrode interface, the number of active sites decreasing sharply with increasing PANI coverage. For thick PANI layers (d > 0.3 mum), silver nucleation occurs with a two orders of magnitude lower nucleation frequency at active sites located most probably at the polymer surface, their number remaining constant for thicknesses up to 1.4 mum. It is established that reduction of the PANI layer occurring in parallel with the silver electrodeposition does not influence the number of active sites for nucleation. The results obtained by interpretation of current transients are in good agreement with results for the number of crystals obtained by microscopic observation. (C) 2003 Elsevier Ltd. All rights reserved.