Alumina, silica and zirconia supported rhodium catalysts were prepared by impregnation and sintered at different temperatures (700-900 degrees C) to obtain metal dispersions ranging from 19-41%. Rhodium oxidation is very sensitive to particle size, the larger the particle size, the higher the temperature of the maximum rate of oxidation, but no significant effect of the support is noted. On the contrary, the reduction of rhodium oxide is less dependent on particle size than oxidation of metallic rhodium, since all the catalysts are reduced in the same temperature range 25-200 degrees C. However, on alumina, the rate of Rh2O3 reduction increases with the mean particle size while on zirconia a contrary effect can be observed, though it is less marked.