Abstract: A process for treating an exhaust stream which includes high levels of noxious compounds containing chemically bound nitrogen, to produce an effluent stream that is extremely low in oxides of nitrogen and environmentally safe for discharge into the atmosphere. A source of oxygen and fuel is added to the exhaust stream to create a fuel-rich mixture, the quantity of fuel being sufficient to react with the available oxygen. The fuel-enriched stream is provided to a thermal reactor and reacted to provide a heated oxygen-depleted stream which includes quantities of by-product NO.sub.x, which stream is then cooled to 800.degree. to 1000.degree. F. Conversion oxygen is added to the cooled stream which is then passed over a first catalyst bed under overall reducing conditions, the quantity of conversion oxygen added being in stoichiometric excess of the amount of NO.sub.x in the stream, but less than the amount of combustibles, whereby the NO.sub.x is first oxidized to NO.sub.2, and then the NO.sub.