The NO/H-2/O-2 reaction has been studied under lean-burn conditions at low temperatures. Maxima in the NO conversions have been observed for a Pt/Al2O3 catalyst at 140 degrees C (50% conversion) and for a 1% Pt/SiO2 catalyst at 90 degrees C (75% conversion). The selectivity to N2O is sensitive to the reaction conditions and decreases as the temperature is raised. Addition of water has a noticeable effect on both the activity and the selectivity for the NO reduction reaction, with N-2 formation being significantly decreased when water is introduced into the reaction mixture. The effect of varying the NO and H-2 concentrations has been examined. In general, increasing the NO concentration lowers the activity, whereas increasing the H-2 concentration increases the activity for NO reduction. The effect of these concentration changes on the selectivity to N2O is complex.