The electroplating of silver and copper has been studied using an electrochemical quartz crystal microbalance (EQCM). Deposition of Ag on Ag follows the expected behavior. For deposition of Cu, the linearity between frequency shift and added mass is maintained, but the slope is smaller (in absolute value). This is attributed to the formation of Cu+ ions, which diffuse in part into the bulk of the solution, without being further reduced. Pourbaix-type diagrams have been developed, showing the regions of thermodynamic stability of the cuprous ions in aqueous solutions, in the absence of complexing agents. In the early stages of deposition of both metals on a gold surface, large deviations of the frequency shift from its calculated value are observed. For Ag, this deviation is due to the difference in the interaction of Au and Ag with the solvent. When Cu is deposited On gold, the deviation is also due to stress in the deposit. This stress, resulting from the difference in crystal parameters between gold and copper, can be relaxed partially at open circuit at room temperature.