Ternary complexes of Co(II), Ni(II), Zn(II), Cd(II), Mg(II) and Ca(II) with adenosine-5′-triphosphate (ATP) as the primary ligand and glycine, alanine, valine, norvaline, leucine, serine, methionine, threonine, aspartic acid, uracil and thymine as secondary ligands have been studied potentiometrically and the formation constants are reported at 35*#x00B7;0=and ¼=0·2(KN0₃). The differences between the stability constants of the ternary complexes and the corresponding binary complexes are expressed quantitatively in terms of the parameter Δlog K. Ternary complexes of all metal ions containing phenylalanine, tryptophan, uracil or thymine have ΔlogK values more positive than expected on statistical grounds, while the ΔlogK values for ternary complexes of all metal ions with glycine, alanine, valine, norvaline, leucine, serine, threonine and methionine are more negative than expected. This trend is more noticeable in ternary complexes containing aspartic acid. Probable explanations for these are provided.