The ability of high- and low-carbon ashes to reduce NO levels in a synthetic flue gas stream has been examined in the temperature range from 350 to 1100 C. High-carbon ash removed all of the NO (up to 340 ppm) from the gas stream, while low-carbon ash had no effect on the NO level of the gases. The carbonaceous material in the ash, possibly in conjunction with CO formation processes, appears to play a major role in the depletion reactions. The gas phase CO, however, does not appear to have a significant role in these reduction processes.