NO and (CO)-C-13 alone and their mixtures as well as the mixture of NO+CH4 were allowed to react with dioxygen on PC/NaX zeolite at different temperatures. It was found that oxygen reacts with NO to NO-O adducts which are held in the zeolite, and are decomposed du:ring the following TPD. (NO)-O-16+O-18(2) exchange proceeds during the isothermal reaction; the gaseous products evolved in TPD contain predominantly unlabelled oxygen of the zeolite lattice. The exchange of oxygen of CO for gaseous labelled oxygens was not found during the reaction under our experimental conditions, but some zeolite oxygens were incorporated into CO2. The CO2 isotopic species become scrambled during the reaction. In the CO+NO reaction the O-2 presence enhances the formation of CO2 but suppresses the formation of N-2. The isotopic exchange of NO with O-18(2) and formation of surface NO-O adducts including lattice oxygens occur even during the interaction of NO with CO. This holds also for the interaction of NO with methane below 230 degrees C, but above this temperature neither the suppression of NO reduction in the presence of dioxygen nor the isotopic exchange of NO+O-18(2) and formation of NO-O adducts were found.