AbstractThe commercial synthetic homopolypeptide polyaspartate (average MW = 30,000, approximately 220 monomers) in solution quantitatively binds up to 40 mol Gd2+ions per mole of polyaspartate. The water proton relaxivity of the solutions is far higher than that of clinically used or commonly investigated gadolinium(III) complexes. It is shown that polymetallic macromolecular complexes combine the high relaxing efficiency of monometallic macromolecular complexes with the favorable metal/ligand mass ratio of small monometallic complexes.