The desorption of CO from the (2 × 1)p2mg layer on Rh(110) was studied by means of a novel method — temperature-programmed X-ray photoelectron spectroscopy (TPXPS). The new information on the variation of the concentration of top and bridge CO during thermal desorption was used to evaluate the difference of the adsorption enthalpies. A model for the structural evolution of the adsorbed layer is suggested, taking into account the CO bonding configurations and the role of the COCO repulsive interactions.