The electrochemical nucleation and growth of palladium particles onto polyaniline (PAni) films have been investigated by chronoamperometry and topographic and phase-mode atomic force microscopy (AFM). The films were synthesized under different potentiodynamic conditions in order to obtain polymer layers with comparable electroactivity but distinctly different morphology/porosity. The analysis of the current transients obtained for the initial stages of the Pd deposition indicates a 3D nucleative formation regime. A detailed Pd electrodeposition study onto the polymer matrix, using different deposition times, suggests that a constant number of critical nuclei is formed in the superficial part of the polymer porous matrix in the time scale between ca. 5 and 15 s. (c) 2007 Elsevier Ltd. All rights reserved.