The binary complexes of H+ and Cu(II) with L-glutamine and L-asparagine were studied by means of a combined potentiometric and calorimetric investigation. The thermodynamic parameters (Delta G degrees, Delta H degrees and Delta S degrees) while on one hand help in understanding the role played by the chain length on the basicity of the amino group, on the other hand do not give a clear-cut answer as to the involvement in the coordination to Cu(II) of the terminal amido group of L-asparagine. A spectroscopic investigation (EPR and UV-VIS) carried out to solve this problem, clearly shows that both ligands are bidentate.