A two-step reduction of Zn(II) ions at the dropping mercury electrode in 1 M NaClO4 + 0.001 M HClO4 with the addition of 3,4-diaminotoluene using an impedance method in wide potential and frequency ranges was examined. It was stated that 3,4-diaminotoluene affected mainly the rate constant of the first electron transfer catalysing the process, but the rate of the second electron transfer changes insignificantly.