The adsorption of CO, the interaction and the reaction of CO and water have been investigated over supported Ir catalysts. The adsorption of CO was studied by infrared spectroscopy. The dominant spectral features for Ir/Al2O3 at 298 K are the bands at 2090, 2060, and 2018 cm(-1) but on Ir/TiO2, Ir/SiO2, and Ir/MgO only a band at 2060-2075 cm(-1) was detected. At higher temperature above 473 K CO induces the agglomeration of Ir, but the H2O hindered this process. In the interaction and in the reaction of CO and water, formate formation was observed on the surface of the catalysts. The IR spectra of the adsorbed CO in the presence of water differed from that observed during the adsorption of CO; the band due to linearly bonded CO was shifted to lower wavenumbers. The reaction of CO + H2O was studied in a fixed-bed continuous-now reactor. The production of H-2, CO2 (with ratio about 1) and small amount of hydrocarbons proceeded readily above 523 K. Ir/TiO2 was found to be the most effective catalyst, its activity was 20 times higher than that of the last effective Ir/SiO2. Possible mechanisms of the CO + H2O reaction are discussed.