The heats of protonation of 12-(2’-hydroxy-benzyl)-1,4,7,10-tetraazazacyclotridecane-11,13-dione (HTADO) have been determined in aqueous solution at 25 +/- 0.1 degrees C and I = 0.1 mol dm(-3) KNO3 by conduction calorimetry. The heats of formation of the binary complex compound of this ligand with Cu(II) and the ternary complex compounds of this ligand with Cu(II)-5-substituted phenanthrolines have also been determined under identical conditions. By utilizing the calorimetric data, the heats of formation of the ternary complex compounds Cu(II)-alpha- amino acids-HTADO have been evaluated through "overall calculation". Some linear enthalpy relationships have been found between the heats of protonation of the ligands and the heats of formation of the ternary complex compounds.