The complexation of the hexapeptide Lys-Cys-Thr-Cys-Cys-Ala (FT), peptidic fragment {56-61}: in the alpha-domain of mouse liver metallothionein I (MT), in the simultaneous presence of Cd(II) and Zn(II) is compared with that of a Zn-containing mammalian MT (Zn-MT II) in the presence of Cd(II). The influence of Cd(II) is studied by square wave voltammetry and differential pulse polarography, at different Cd:Zn:FT molar ratios, which yield a rough picture of the metal exchange processes taking place. The application of multivariate curve resolution with alternating least squares optimization (MCR-ALS) allows both the unitary voltammograms and the concentration profiles to be obtained. Moreover. MCR-ALS is applied for the first time to the study of the complexing properties of a complete MT. On the basis of these results, the electrochemical reduction processes and some structures are depicted for the chemical species considered in the mixed metal system Cd Zn FT. In the case of Cd-Zn-MT II, additional information is required before proposing similar models.