In view of a possible application to aluminium(III) chelation therapy, 3-hydroxy-4-pyridinecarboxylic acid (3H4P) and 4-hydroxy-3-pyridinecarboxylic acid (4H3P) were synthesised, and their chemical interactions with the metal ion were investigated in aqueous 0.6 m (Na)Cl at 25°C by means of potentiometric titrations. Only mononuclear complexes of the type AlL l H h (l = 1, 2 and 3; h = 0, 1, ..., l) were formed. The qualitative and quantitative results obtained were confirmed by UV spectrophotometry and 1 H NMR spectroscopy. The efficiencies of the ligands to chelate aluminium(III) were evalu-