The effect of water and reductants (CO and H-2) on the decomposition of NOx stored on BaO/Al2O3 at 300degreesC has been investigated. Water eliminates the initial rapid total uptake of NO2 but has little effect on the subsequent formation of nitrates that is accompanied by evolution of NO. Water hinders liberation of NO2 and NO during temperature-programme decomposition of stored NOx. Both CO and H-2 lower the temperatures required for decomposition through reduction of NO2 to NO and N-2 thus restricting NO2 readsorption. The rate of reduction is lower with H-2 than with CO.