Copper ions were introduced in a Na-ZSM-5 zeolite by using exchange, impregnation and precipitation procedures. The catalytic activity of the three solids was measured in the reduction of NO by propane in the presence of oxygen (0 to 10 vol.-%) in the 423-773 K temperature range. At a given temperature the activity for nitrogen formation remarkably increased with the oxygen content in the 0.5-2 vol.-% range, then slightly decreased for higher amounts of oxygen. For an oxygen content exceeding 0.5 vol.-% and regardless of the reaction temperature, the Cu-ZSM-5 sample prepared by exchange was the most active catalyst, the catalytic activity being expressed per gram of introduced copper. The adsorption of carbon monoxide followed by FT-IR spectroscopy suggested that copper was present as isolated Cu+ ions in the three catalysts. The dispersion of cuprous ions was the highest for the sample prepared by the exchange process. The catalytic activity appeared related to a high dispersion of isolated Cu+ ions in the MFI framework.