Electrodeposition of noble metals that can be used as catalysts of chemical and electrochemical reactions is a process of major importance both from a practical and a scientific point of view. This is particularly true for the very initial stage of the phase transition comprising nucleation and growth phenomena leading to the formation of a highly dispersed metal phase with a strongly developed active surface area. The paper contains information on the nucleation and growth stage of platinum electrodeposition on an oxidised titanium working electrode. Cathodic current transients are recorded under potentiostatic conditions and are analysed in terms of the theory of progressive nucleation with overlap of diffusion zones and limited number of active sites. Data are obtained on the diffusion coefficient D of the platinum ions, on the nucleation rate constant A and on the number No of active sites on the titanium surface.