A combined monolithic catalytic system has been developed by which NOx and SOx are successively removed from flue gases produced by the combustion of coal and other fossil fuels. The honeycomb catalysts used in this study have been manufactured at industrial scale by extrusion of pastes which contain all the precursors or their components. Nitrogen oxides are removed in the first stage of this combined process by selective catalytic reduction with ammonia, using a DeNO(x) monolithic catalyst based on Ti-V-W oxides dispersed in the structure of a natural magnesium silicate. The outlet gases pass through a second monolithic bed which oxidizes SO2 to SO3; this DeSO(x) monolithic catalyst is based on vanadium oxides and alkali pyrosulfates supported on diatomaceous earth. Laboratory scale activity tests were carried out using small honeycomb sections cut from the industrial catalysts. At a temperature of 450 degrees C, molar conversions of 90% and 80% for NOx and SOx were achieved respectively, without any ammonia slip. The monolithic structure, and mechanical properties of both catalysts allows their operation in high dust configurations.