The adsorption of CO and H(2) at the surface of transitional (gamma and delta) and corundum (alpha) phases of Al(2)O(3) is studied by means of FTIR spectroscopy at temperature variable in the 293-60 K (CO) and 293-20 K (H(2)) intervals with the aims of better clarifying the nature of the surface Lewis centres and evaluate the thermodynamics of the adsorption process.