The electrochemical behaviour of 2,4-dinitrosoresorcinol (DNR) on Pt and Au electrodes modified by underpotentially-deposited heavy metal monolayers was studied in aqueous HClO4 solutions. At these modified electrodes, DNR is reduced to 2,4-diaminoresorcinol. The reduction wave of this eight-electron reaction is diffusion-controlled. This process proceeds through hydroxylamine intermediates whilst an azoxy derivative is formed by a condensation reaction between DNR and the dihydroxylamino intermediate. The reduction and oxidation of tetraoxime of 1-cyclohexene-3,4,5,6-tetrone (TCT) was also studied on Pt surfaces covered by heavy metal monolayers. The reduction of TCT is a 12-electron reaction yielding phenylene-1,2,3,4-tetramine. The reduction of this cathodic process also exhibits diffusion-controlled character. The oxidation of TCT is a four-electron reaction producing 1,2,3, 4-tetranitrosobenzene which is rapidly converted to the tautomeric form benzobifuroxan.