During a differential pulse polarographic determination of selenium, the selenite peak was diminished upon the addition of some ions, such as lead, copper and cadmium. On the other hand, the addition of selenite ion had the same effect on the peaks of the mentioned ions. In both cases a new reduction peak appeared at a more positive potential with respect to the selenite and present ion reductions. This observation is attributed to an intermetallic compound formation between selenium and the ions present. The peak is brought about by a reduction of the lead ion, which afterwards forms an intermetallic compound with selenium adsorbed on the mercury-drop surface (Pb2++Se-(ads)+2e reversible arrow PbSe(ads)). Temperature-dependence studies also revealed that the observed phenomenon is a surface reaction.