The binary and ternary complexes of some M(II) ions with dicarboxylic aliphatic acids as primary ligands and some triazole compounds as secondary ligands have been studied pH-metrically in aqueous media at 25 degreesC and at a constant ionic strength of I = 0.10 mol dm(-3) (KNO3). The formation of the different 1:1 binary and 1:1:1 ternary complexes is inferred from the corresponding titration curves. The stability constants of the different complexes formed were determined and are discussed in terms of the nature of both the ligand and metal ion used. The stability of the ternary complexes is also discussed in relation to that of the binary complexes of secondary ligands.