Experiments have been performed using pulsed high-voltage discharges with the aim of removing NO and SO2 from flue gas obtained from a methane burner. It is found that the NO conversion is strongly increased by the addition of SO2 or NH3. When both gases are added simultaneously the increase almost disappears. The synergetic effect can be maintained, as is shown, when NH3 is introduced much later than SO2. The SO2 removal is already 70% upon stoichiometric addition of NH3, but the electric discharge improves this to >95% and reduces the NH3 leak to a few ppm. This increase is probably related to aerosol production by the pulsed discharge which enhances the ammonium salt production. A so-called “history effect” is observed, i.e., the removal of NO and SO2 depends on the time that is taken to reach the required energization. It appears that the discharge has to create favorable conditions for the cleaning process. Using the synergetic and history effects the best cleaning result, at initial concentrations of 300 ppm, is 80% NO removal and 95% SO2 removal with 3 ppm NH3 leak. In this case the energy cost is 13 eV/NO (or a yield of 90 g NO and 200 g SO2 per kWh). Possibilities for further improvement are indicated.