Cobalt and nickel in aqueous solutions can be determined by adsorptive striping voltammetry, using dimethylglyoxime as a complexing agent in order to accumulate the metals efficiently on a mercury surface. In borate buffer solution (pH 9.3) capacity results suggest that Co(II)-dimethylglyoxime (Co(HDMG)(2)) adsorbs in. two different orientations each undergoing different reaction pathways: for low surface concentrations Co(0) is produced and two electrons are transferred; for high surface concentration both Co(II) and the ligand are reduced, this process involving the transfer of more than two electrons.