Solution equilibria of the binary and ternary systems involving Mn+ ion, adenosine 5‘-triphosphate, and some mono- and dicarboxylic amino acids (Mn+ = CuII, NiII, CoII, LaIII, and CeIII) have been investigated potentiometrically at (25 ± 0.1) °C and I = 0.10 mol dm-3 (KNO3). The formation of the different binary and ternary complexes is inferred from the corresponding titration curves. The stability constants of the various complexes formed were determined and discussed in terms of the nature of both the metal ion and the ligand. Moreover, the stability of the mixed ligand complexes is discussed in relation to that of the corresponding binary complexes of amino acids.