The reduction of N2O by CO on polycrystalline foils of Pt, Pd and Rh was studied in the range 10(-6) less-than-or-equal-to p(i)/mbar less-than-or-equal-to 10(-3) and 250 less-than-or-equal-to theta/degrees-C less-than-or-equal-to 600. It is inhibited by CO at temperatures lower than 300-degrees-C. Additionally, isothermal oscillations of the reaction rate were observed on Rh at temperatures below 320-degrees-C. Above 450-degrees-C the reaction rate on Pt and Pd is independent of CO pressure and first order with respect to N2O. On Rh the reaction is first order with respect to the compound the pressure of which is less. The reaction between CO and O-2 is favoured for all catalysts, temperatures and compositions if oxygen is present in the system.