Complex formation in the ternary systems M(n+) + dipicolinic acid + amino acids or N-(2-acetamido)-iminodiacetic acid (H(2)ADA), where M(n+) = Cu-II, Zn-II, Ni-II, Co-II, Hg-II, Cd-II, Pb-II, UO2II, Y-III, and Ce-III, have been investigated pH-metrically in aqueous media at 25 degrees C and at ionic strength I = 0.10 mol dm(-3) (KNO3). The stability constants of the different binary and ternary complexes formed in such systems have been determined and discussed in terms of the nature of both metal ion and secondary ligand (amino acids or H(2)ADA). It was deduced that, except in the case of dicarboxylic amino acid, the stability of the ternary complex is lower than that of the corresponding binary M(n+) + amino acid or H(2)ADA.