A plateau of a limiting current observed on voltammograms in the ligand-deficient Cu/Cu(II) ethylenediamine system is a prewave resulting from abrupt changes in the solution composition at the electrode surface. Voltammograms may be described quantitatively by equations of formal kinetics accounting for two consecutive one-electron transfers provided that the process of Cu2+ + e(-) --> Cu+ is a rate-determining step. Cu2O developed under open-circuit conditions exhibits properties typical of an adsorbed layer. The exchange current density of Cu(II) reduction decreases with the thickness of such layers. The irreversible reduction of Cu2O occurs at sufficiently high cathodic overvoltages, resulting in a significant activation of the electrode surface.