CuOx-modified and unmodified Mn2O3,Cr2O3 and WO3 catalysts were prepared by impregnation with Cu(NO3)(2) solution and/or calcination at 700 degrees C of appropriate precursor compounds. Bulk phase composition and thermochemical stability were characterized by X-ray diffractometry, infrared spectroscopy and thermogravimetry. The surface area, chemical composition, oxidation state and chemisorption capacity were determined by X-ray photoelectron spectroscopy and sorptometry of N-2, O-2 and CO gas molecules. The catalytic CO oxidation activity was tested, using a gas circulating system equipped with a fixed-bed microreactor and a gas chromatograph. The CuOx additives were found to promote markedly the otherwise insignificant CO oxidation activity of WO3 at 250-400 degrees C. This was related to concomitant improvement primarily in the lattice oxygen reactivity, and in the O-2 chemisorption capacity. The already high CO oxidation activities of Mn2O3 and Cr2O3 catalysts at 150-250 degrees C were found to be, respectively, slightly and hardly improved by CuOx additives, despite a marked improvement in oxygen chemisorption capacity. This was attributed to establishment on the unmodified catalysts of a favourable electron-mobile environment. In oxygen-rich reaction atmosphere, both the modified and unmodified catalysts were thermochemically stable. However, in lean oxygen atmosphere, Cr2O3 and CuOx-modified WO3 were relatively the most stable test catalysts.