A model is proposed for the voltammetry of metal ions in mixtures of macromolecular and simple ligands. Among other hypotheses, the model assumes excess of ligand and absence of both electrodic adsorption and kinetic effects (complexes are supposed to be totally labile or totally inert). The mathematical solution of the model provides general equations which are used for simulation purposes. Besides that, the limiting case when only 1:1 labile complexes exist is extensively discussed and the resulting equations applied to the polarographic study of the systems Zn(II) + polymethacrylic acid + phthalate and Cd(II) + polymethacrylic acid + bromide.