The involvement of the omega -NH2 terminal group of L-lysine and L-ornithine in the complexation of Cu(II) was investigated by means of potentiometry, calorimetry, UV-Vis and ESR. The thermodynamic parameters (DeltaG(0), DeltaH(0) and DeltaS(0)) obtained by combining the potentiometric and calorimetric data show that the two ligands complex copper(II) in a different manner, indicating that the omega -NH2 terminal group is involved in ornithine complexes only. UV-Vis and ESR spectra further support the involvement of ornithine omega -NH2 and provide details on the complexation geometries of the complexes of the two amino acids.