The oxidation of CO in the presence of hydrogen (PROX process) was investigated on bimetallic Au-Rh catalysts at 300-373 K by Fourier transform infrared spectroscopy and mass spectroscopy. The effects of catalyst composition, reaction temperature and composition of the reacting gas mixtures have been studied. The IR studies revealed the formation of bi- and monodentate carbonates, bicarbonates and hydrocarbonates on the catalysts surfaces; these surface species proved to be not involved in the surface reactions. The formation of adsorbed formaldehyde was observed on all surfaces, except 1% (0.25Au+0.75Rh)/TiO2. Adsorbed CO2 (as the surface product of CO oxidation) was not detected on any surface. The presence of both O-2 and H-2 reduced the surface concentration of CO adsorbed on the metallic sites. Mass spectroscopic analysis of the gas phase showed that gaseous CO2 was formed in the highest amount in the CO+O-2 mixture, the presence of H-2 suppressed the amount of CO2 produced. This negative effect of H-2 was the lowest on the 1% Rh/TiO2 and 1% (0.25Au+0.75Rh)/TiO2 catalysts.