A consistent method for the calculation of the electric current through a redox-mediated electrochemical tunnel contact with two redox groups in the bridge molecule is presented for the sequential mechanism of electron transfer in the limit of infinitely large Coulomb repulsion between the electrons located in the same redox group. It is shown that the kinetic inter-group correlation exists which results in general in the deviation of exact solution from the approximate "quasi-chemical approach" even in the absence of inter-group Coulomb repulsion. The increase of the latter leads to the appearance of the electron correlation effects which result, in particular, in the second maximum (Coulomb blockade peak) in the current/overvoltage dependence. (C) 2009 Elsevier Ltd. All rights reserved.