The paper presents the results of electrochemical investigations of copper deposition from a sulfate/sulfuric bath of industrial relevancy and containing two additives. In particular the effect of chloride ion with polypropylene ether (LP-1(TM)) could be highlighted by voltammetry and impedance measurements. When used without chloride ion LP-1 adsorbs at the surface which reduces significantly the current density and the double layer capacitance. A current peak was observed for the simultaneous presence of the two additives and this was attributed to a sudden inhibition of the surface : in a narrow range of potential Cl-complexes were assumed to desorb from the surface, allowing significant adsorption of inert LP-I molecules. Besides, kinetic parameters and the diffusion coefficient of cupric ion were correlated to the concentrations of additives, copper sulfate and sulfuric acid in a broad range of concentration.