A new method for the calculation of rate constants of homogeneous reactions following an electron transfer step (the so called EC or electrochemical-chemical mechanism) is presented. It is shown that the diffusion problem for cyclic voltammetry for an EC mechanism has an analytical solution for a fast electron transfer reaction and an irreversible subsequent homogeneous reaction, provided the concentration of electroactive species does not change considerably during the voltammetric scan. This condition corresponds to analysing the voltammogram for current densities far below the peak current density. It is shown that the rate constant can be easily derived from the sweep rate at which no current minimum is observed in the reverse sweep. The rate constant for the reaction between Cu(I) and H2O2 has been measured with this technique and a value of (75+/-10) dm(3) mol(-1) s(-1) has been found.