The electrochemical response of the peptidic fragment Lys-Cys-Thr-Cys-Cys-Ala [56-61] MT I (FT) in the presence of zinc was investigated by cyclic voltammetry using a hanging mercury drop electrode. For a given concentration at the ratio of [Zn]:[FT] = 1:1, the influence of scan range, scan rate and concentration was studied. The variation of the initial potential, allowing or avoiding the oxidation of the mercury electrode in the presence of thiol groups complexed by zinc, modifies the concentration of compounds near the electrode and consequently the voltammogram features. The evolution of the complexation equilibrium, attained by successive additions of Zn2+ to a sample of FT, was followed by the negative scan of voltammograms recorded at the first cycle and at an initial potential of -0.55 V at which the oxidation of the mercury is avoided.