Catalytic reduction of NO in the presence of water and oxygen has been studied on mechanical mixtures of La0.59Sr0.39MnO3 with quartz or aluminas. Though practically inactive alone when alumina is added to the manganite a significant increase in NO reduction activity is observed. The ＇cooperative effect＇ can be explained by the presence of dilutant on NOx- adsorbed species involved in N-2 formation.