Nucleation and growth of spherical clusters is considered in case of multi-step electrochemical reactions and ions' direct attachment mechanism. Theoretical expressions describing the time dependence of the clusters' linear size and growth current are derived accounting for complete charge transfer and combined charge transfer and diffusion limitations. Progressive and instantaneous nucleation is examined too and theoretical formulae are derived for the current-time relationships in both cases. (c) 2007 Elsevier B.V. All rights reserved.