The anodic stripping potentiometric (ASP) determination of antimony on a combined working-auxiliary-reference electrode system is described. The method utilises 3 M HCl as supporting electrolyte and a combined glassy carbon mercury film electrode at an electrolysis potential of -400 mV versus Ag-AgCl (1 M HCl) for the reliable determination of ultratrace concentrations of antimony. A detection limit of 0.3 μg l-1 and a linear concentration range of 0.3-150 μg/l-1 antimony were accomplished under these conditions with an electrolysis time of 10 min. The use of L-cysteine was effective for the reduction of Sb(V) to Sb(III) and its subsequent use for the ASP determination of the metalloid. The method was successfully applied to the determination of trace and ultratrace concentrations of antimony in water and orchard leaves samples.