The influence of a reducing atmosphere on the thermal stability of CeO2 was studied on a high surface area ceria sample (115 m(2) g(-1)) treated 2 h under hydrogen or carbon monoxide at various temperatures between 673 and 1123 K, Comparative experiments were done under air or vacuum, and also in presence of water or carbon dioxide in order to estimate the relative importance of the reduction products. An important decrease of the specific surface area was observed between 850 and 1000 K under air, vacuum, carbon monoxide or water pressure, the residual BET area being below 10 m(2) g(-1) at 1100 K, Under hydrogen, the same loss of surface was obtained at ca. 150 K lower temperatures, In all cases, the first step was the elimination of the microporosity followed by the growth of the crystallites. The peculiar influence of hydrogen was related to the high concentration of lattice oxygen vacancies created during the reduction of the bulk. In the case of carbon monoxide atmosphere which also reduces the sample, the carbonate species formed during the reduction are eliminated from the bulk at higher temperatures, which explain the better resistance to sintering compared to hydrogen. This was confirmed by a treatment under carbon dioxide atmosphere which was found to preserve the specific surface area better because of the stabilization of the carbonate species on the ceria.