Solution equilibria of the ternary systems of Zn-II, Ni-II, Co-II, Cd-II, Pb-II, UO2(II), Ce-III, and La-III with N-[tris-(hydroxymethyl)methyl]glycine (tricine), N-(2-acetamido)iminodiacetic acid (H(2)ADA), and dicarboxylic amino acids (aspartic and glutamic) as primary ligands and 3-amino-5-mercapto-1,2,4-triazole as a secondary ligand have been studied pH-metrically at (25 +/- 0.1) degreesC, and a constant ionic strength I = 0.1 mol dm(-3) (KNO3). The formation of various binary and ternary complexes has been inferred from the corresponding titration curves. The stability constants of the different complexes are determined and discussed in terms of the nature of both the ligands and metal ions.