Recently, the highly specific and sensitive technique of adsorption voltammetry has been developed for ultra-trace metal determination. the method involves adsorption of a ligand at an electrode, accumulation of the metal as an adsorbed complex and reduction of the adsorbed metal complex. In this work, the differential pulse adsorption voltammetric method for the determination of cobalt and nickel has been examined to determine whether adsorption voltammetric methods are likely to provide equivalent data to the widely used methods based on anodic stripping voltammetry when applied to speciation studies in natural water systems. Importantly, in contrast to anodic stripping methods for the determination of copper, lead and cadmium in natural waters, data for cobalt and nickel are essentially independent of the presence or absence of ultra-violet irradiation pretreatment methods aimed at removing dissolved organic material. It is therefore suggested that dimethylgloxime, the organic reagent used in the adsorption voltammetric method for determination of cobalt and nickel, enables the detection not only of labile nickel and cobalt complexes of the kind determined in anodic stripping voltammetry but also of the majority of organically bound cobalt and nickel complexes. That is, the high stability constants and specificity of dimethylglyoxime towards cobalt and nickel enables essentially total metal concentrations to be determined. From this result, it is suggested that all speciation studies on natural water systems undertaken via adsorption voltammetric methods will need to be assessed critically to establish whether total metal or specific forms of the metal are being determined. That is, because anodic stripping and adsorption voltammetric methods are based on fundamentally different principles they need not necessarily provide equivalent data in the area of trace metal analysis.