The heterogeneous electron transfer reaction for the reduction of some nitroso aromatic derivatives in aqueous-alcoholic medium was studied on both mercury and glassy carbon electrodes (GCE) by using cyclic voltammetry (CV) and scanning electrochemical microscopy techniques (SECM). The nitrosoaromatic derivatives followed a two-electron two-proton mechanism producing a quasi-reversible overall process. This strongly pH dependent mechanism varied from ECCE mechanism at pH < 8.5 to ECEC mechanism pH > 8.5. The apparent heterogeneous rate constant for the reduction of the nitroso derivatives was calculated using CV or SECM. The rate constant for the electron transfer process depends on the nature of the electrode material. The heterogeneous rate constant on the GCE is almost two orders of magnitude smaller than that on mercury electrode i.e. (3.4 +/- 0.3) x 10(-3) cm s(-1) on Hg and (7.0 +/- 1.0) x 10(-5) CM s(-1) on GCE, for the same nitroso compound and pH. The heterogeneous rate constant values were checked by comparison between experimental and simulated cyclic voltammograms. (c) 2007 Elsevier Ltd. All rights reserved.