The formation of the Rh-I ion during CO chemisorption on Rh/Al2O3 catalysts has been directly observed using W-visible spectroscopy. Comparison of infrared and UV-visible spectra indicates that the species Rh-I(CO)(2) is produced by a surface oxidation process operating on metallic Rh-0 sites and involving Al-OH groups as oxidizing centers, in agreement with previous postulates.