The transition phenomena in metal deposition processes have been studied in the system Ag(hkl)/Pb '+ by potentiostatic pulse experiments from the underpotential to the overpotential range. The analysis of the current-time trandents indicates a model of' progressive nucleation and hemispherical ditfusion to the growing 3-D crystallites. An important influence of the initial state in the underpotential range on the nucleation rate has been found. Furthermore, the nucleation rate strongly depends on the overvoltage and on the substrate nature. All experimental results are explained by a stepwise bulk phase formation process including rearrangement of adatoms in the 2-D adsorbed layer, formation of critical clusters and further rearrangement and growth forming epitaxially ortentated 3-D crystallites. The nucleation process must be treated by an atomistic model due to the derived low number of atoms in the critical cluster. * Merck, Darmstadt. * Bank, GBttingen, for macro-crystals and Prof. Dr. K. Roe, Portland University, OR, USA; for micro-crystals. $ MI'-IM 400, Megaphysik, Rastatt. § Explorer III with floppy disk. Nlcolel, Madison. ' HP, Type 9845 T. Opt. 250, Floppy disk HP 9895 A and Plotter HP 9872 B.