A process is described for reducing the NO.sub.x concentration and N.sub.2O concentration from the residual gas from nitric acid production. The process encompasses the passing of the residual gas leaving the absorption column, prior to entry into the residual gas turbine, through a combination of two stages. The first stage here reduces the NO.sub.x content and the second stage the N.sub.2O content of the gas, the NO.sub.x/N.sub.2O ratio prior to entry of the gas into the second stage being in the range from 0.001 to 0.5, and this gas being brought into contact in the second stage with a catalyst which is substantially composed of one or more iron-loaded zeolites.