The first stages of the zinc electrodeposition process on highly oriented pyrolytic graphite (HOPG) from a 0.1 M ZnSO4 + 0.5 M Na2SO4 solution were analyzed in the absence and in the presence of gelatine as additive, using cyclic voltammetry, potentiostatic current transients and atomic force microscopy. In the solution free of gelatine the zinc deposition can be interpreted by a model involving instantaneous nucleation on active sites and diffusion-controlled 3D growth. In the solution containing gelatine the HOPG surface is partially covered by a gelatine film which blocks the steps edges and surface defects, decreasing the nucleation rate and affecting the nucleation mechanism. The morphology of the Zn crystals formed would be also affected by the gelatine adsorption in the first stages of deposition. (C) 2003 Elsevier B.V. All rights reserved.