The voltammetric reduction of Ni-II(DMGH)(2) complex preadsorbed on mercury both in 1 M NH4Cl + NH3 buffer and in 0.1 M borate buffer solutions was studied. In this work experimental evidence points to Ni-II(DMGH)(2) reduction with simultaneous decomposition of the ligand DMGH(-) and reduction of Ni(II) to Ni(O). The experimental sweep rate dependence of peak current and potential is explained in terms of a ErCi surface reaction scheme and a rate expression that takes into account attractive forces between the adsorbed reactant complex.