The transfer of heavy metal ions across the polarized nitrobenzene \ water interface assisted by 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (DPT) present in the nitrobenzene phase has been studied by normal pulse voltammetry and cyclic voltammetry. Voltammetric waves of Pb2+ and Cd2+ ions were reversible, whereas that of Zn2+ ion was quasi-reversible. Voltammetric waves of Hg2+, Fe2+, and Co2+ ions were more or less irreversible. The voltammogram of Cu2+ ion showed a two-step wave. The dependence of the reversible half-wave potentials of Pb2+, Cd2+, and Zn2+ ions on the concentration of DPT in the nitrobenzene phase reveals that their ion-transfer is assisted by the formation of 1:n metal-DPT complex(es) in nitrobenzene; Pb2+ : n = 3 and 4 with the formal formation constants (log beta(n)(O)) of log beta(3)(O) = 18.2 +/- 0.1 and log beta(4)(O) = 20.4 +/- 0.1; Cd2+: n = 3 with log beta(3)(O) = 27.1 +/- 0.1; and Zn2+: n = 3 with log beta(3)(O) = 36.0 +/-0.1, respectively.