The selective reduction of nitrogen oxide by various hydrocarbons has been investigated with alumina-and silica-supported Pt catalysts. Significant variations are observed in the effectiveness of the reductant, with n-paraffins being the most effective and iso-paraffins the least effective for alumina-supported catalysts. Silica-supported catalysts show higher activities, especially with iso-paraffins. n-paraffins are found to be effective at low temperatures whereas toluene is more effective at higher temperatures. Particle size effects for alumina-supported catalysts do not appear to have much influence for the reactions involving toluene. An interesting feature is the absence of nitrous oxide formation when toluene is used as the reductant.