Abstract: In the buffers of HOAc—NaOAc (pH 6) or Na₂B₄O₇—NaOH—NaOAc (pH 9～10), EDTA gives an incision on dE/dt-E curve, which can be used to determine the end-point of titration of oscillopolarographically inactive metal ions, when mercury film electrode is used. In 0.01 N NaOH solution, the incision on dE/dt-E curve due to EDTA is too ambiguous and cannot be used in titration, but the incision on the dE/dt-t curve is very sharp and sensitive and can be used to determine the end-point of EDTA titration of calcium gluconate. In NH₄OH-NH₄Cl buffer solution, both anode and cathode incisions of Zn⁺⁺ on dE/dt-t curve are sensitive and sharp. Therefore, sometimes dE/dt-t curve is better than dE/dt-E curve.