Acid-base characteristics of a series of rubidium- and strontium-modified materials were studied using adsorption microcalorimetry of ammonia and carbon dioxide. The samples were prepared by impregnation and decomposition of acetate precursors at 773 K on gamma-alumina, titania, carbon, and silica. Microcalorimetric measurements showed that the incorporation of rubidium and strontium neutralized acid sites and created new base sites on the supports. However, the extent of these modifications depended on the compositions of both the basic additive and the support. Rubidium was more effective than strontium at altering the acid/base character of all the supports studied. The fewest base sites were found on modified silica, presumably due to the formation of surface silicate phases.