A modified carbon paste electrode that specifically reacts with Hg-2(2+) ions in a Hg2+ and Hg-2(2+) mixed solution has been constructed by incorporating picolinic acid N-oxide into graphite powders. After a preconcentration in a Hg-2(2+) and Hg2+ ion (pH 2.0), this electrode shows a well-defined anodic stripping peak for only Hg-2(2+) ion and a linear response between 3.0 x 10(-8) M and 1.0 x 10(-6) M of Hg-2(2+) ion. The electrode has been successfully applied to the selective determination of trace Hg in the human urine sample.