This paper investigates the chemical and electrochemical properties of copper species in the molten eutectic mixture Na2CO3 + K2CO3 at 800 degrees C. In melts equilibrated with gas phases containing O-2 and CO2 with partial pressures of O-2 ranging from 8 x 10(-3) to 3.3 x 10(-1) at. and with a total pressure of 1 at., copper always dissolves as a mixture of Cu(I) and Cu(II), whether Cu2O or CuO is used as solute. Both Cu(II) to Cu(I) and Cu(I) to Cu(O) reductions can be detected in the electrochemical stability range. In the case of cyclic voltammetry, the positive scan was found to yield, successively, scarcely soluble Cu2O and Cu(II). In the melt investigated, the total solubility of copper, which is probably that of Cu2O, was found to be 10.5 g(Cu) 1(-1). The influence of the composition of the gas phase on the redox ratio [Cu(II)]/[Cu(I)] was also investigated. Analysis of the experimental results with reference to the equilibrium between the O-2/CO32-/CO2 and Cu(II)/Cu(I) redox systems allows the occurrence of at least one copper oxyanionic species to be assumed. Cu+ and CuO22- are proposed as solvated species.