The standard rate constant of a simple electrode reaction Ox + ne- ↔ Red, in which both Ox and Red are solution soluble, can be determined by the variation of frequency in the square-wave voltammetry with inverted scan direction: log ks = log f01/2 + log D1/2 - 0.60 ± 0.01. In this equation log f0 is the abscissa of the intersection of straight lines Ep, 2 = a log f + b and Ep, 2 = E0, where Ep, 2 is the potential of the second peak of the net response, E0 is the standard potential, a = 2.3RT/2(1-α)nF, b = E0 - 2a log ks + a log D – 0.0353/(1-α)n and D is a common diffusion coefficient.