Complexes of nickel(II) and zinc(II) with L-cysteine and D-penicillamine were investigated by pH-metric, spectrophotometric and magnetic measurements. The formation of polynuclear species M3A4 was proved in the case of L-cysteine. Both ligands can also form protonated complexes. The concentration of mixed species is higher in the systems containing the zinc(II) ion. Mixed ligand complexes were not identified in the nickel(II)-D-penicillamine-glycine system. With L-histidine or histamine as ligand B, the formation of mixed ligand complexes was detected in spite of the different structures of the parent complexes. The stability constants of the mixed complexes of zinc(II) closely corresponded to statistical expectation.