The reactions of copper on Au(111) electrode in the underpotential deposition (UPD) region from chloride media were investigated by cyclic voltammetry. Chloride concentrations ranged from trace levels up to 0.55 M. At chloride concentration below 10(-3) M three different adlayer structures were detected. At least one of these structures also contains perchlorate ions besides copper and chloride. At NaCl concentrations above 5 x 10(-3) M, Cu(I) is stabilized by chloride. and the reduction of copper proceeds as one electron process on the Au(111) surface covered with copper and chloride bilayer but not on Au(111) free of copper.