It is shown that the reduction of Cd(II) can be studied using the dropping mercury microelectrode (DM mu E) so that the preceding chemical step is kinetically fully rate-determining. Consequently its rate constant can be obtained with good accuracy, which allows us to show that its weak potential dependence can be explained quantitatively using simple double-layer theory. The DM mu E voltammogram is shown to vary with base electrolyte concentration in accordance with these ideas.