Ternary 1:1:1 complexes of YIII, CoII, NiII, CuII, LaIII, CeIII and UO 2 2+ with N-(2-acetamido)iminodiacetic acid (H2ADA) as primary ligand and salicylic, anthranilic or phthalic acid as secondary ligand are described. The complexes of CoII and CuII were isolated and characterized by microanalysis, molar conductance measurements, thermal analysis, i.r. and u.v.-vis. spectra. The formation constants of the 111 ternary complexes were determined potentiometrically in 20% (w/w) EtOH-H2O at 24 °C. The stabilities of the 111 M n+ :ADA2–:aromatic acid ternary complexes are higher than those of the corresponding 11 M n+ :aromatic acid binary complexes.