The kinetic study of the internal oxidation of dilute Ag-Cu alloys has made it possible to reveal state of preoxidation characterized by very great hardness and by a very great residual resistivity, a dilation of the lattice, and an oxygen weight gain greater than that corresponding to the formation of the oxide CuO. To interpret this stage of preoxidation, we have considered the formation of complexes of the CuO type, resulting from interaction among copper atoms in substitution and oxygen atoms in insertion.