The development of a catalytically active ceramic filter element for the combined removal of particles and nitrogen oxides from gas streams is presented. A special catalyst support layer with a high BET surface followed by optimized catalytic activation was developed to reach the required nitrogen oxides (NOx) emission levels. The catalytic properties of the developed filter element were studied in detail in a small test rig using cylindrical filter segments. The catalytic filter elements were tested under different operating conditions, Such as filtration velocity, operating temperature, and nitrogen oxide (NO) inlet concentrations. Moreover, the filtration properties of the filter elements were determined. As result Of these studies, the optimum operating conditions for the catalytic filter element are determined with respect to a minimum differential pressure value in combination with a high catalytic activity towards NOx removal. The advantages and possibilities of the newly developed filter elements are shown and discussed. (C) 2007 Elsevier B.V. All rights reserved.