A multivariate curve resolution method by alternating least-squares (MCR-ALS) is applied to differential pulse voltammograms measured on the Cd(II) + (gamma-Glu-Cys)(2)Gly system as a model of metal-phytochelatin interactions at concentrations of both components in the range 10(-7)-10(-5) mol 1(-1.) The course of complexation is different when peptide is titrated with metal from that when metal is titrated with peptide. The combined analysis of both matrices from titrations of peptide with metal and of metal with peptide allowed the resolution of the system. The analysis of the resulting pure voltammograms and concentration profiles of the resolved components suggested the presence of four different types of bound Cd(11) and made possible the formulation of a complexation model.