Derivative control was applied to electrochemical oscillators under potentiostatic as well as galvanostatic conditions; i.e., the time derivative of a measured quantity (such as the current or the concentration of an electrochemical species) is fed back to the externally applied voltage or, respectively, current. In particular cases the control led to stabilization of the unstable node, i.e., suppression of oscillations. By comparison with model calculations, it is shown that the result of the derivative control provides valuable information about the mechanism of an electrochemical oscillator and the role of certain species.