General explicit expressions are presented for the current I-p corresponding to the pth step of any sequence of potential steps E-1, E-2,...,E-p, when both oxidised and reduced species are present initially. These equations are applicable to reversible processes at planar and spherical electrodes whose areas increase with any power of time (A(t) = A(0)t(z), z = 0 for planar and spherical static electrodes and microelectrodes, and z = 2/3. for the DME). For an SMDE we have also considered those situations in which the diffusion coefficient values, of both species are not equal and the reaction product is amalgamated initially into the electrode. As an example of the application of these equations, we have analysed the influence of the presence of the reaction product in multistep chronoamperometry for an SMDE and also when microhemispheres are used by considering that the diffusion coefficients are equal and the product is soluble in the electrolytic solution. All equations are applicable to any single, double or multipotential step techniques and also to linear sweep and cyclic voltammetry and polarography: