A method for determining electrochemically active complexes reacting on the electrode is proposed. The mechanism of zinc discharge from iminodiacetate electrolytes is discussed as a specific example. The distribution of complex species on the electrode surface and relations of electrochemically active complex formation were determined. It is shown that monoligand and hydrated zinc(II) ions are electrochemically active and that Zn(Imda)(2)(2-) does not react on the electrode under the experimental conditions. The discharge of this ion is retarded by the preceding chemical electrode stage of dissociation.