Experimental data on current oscillations observed during copper and tin codeposition from solutions involving Laprol 2402C as a surface-active substance, confirm an idea of the usefulness of impedance spectroscopy data for predicting the stability features of electrochemical systems. An analysis of the impedance data obtained for the negative slope region of the voltammogram allows to establish the value of the external resistance at which oscillations are generated and to estimate frequencies of these oscillations, No hidden negative impedance and, therefore, no potential oscillations at controlled current were found.