The invention relates to a method for producing an NO/N2 gaseous mixture, comprising the steps of effecting a purification of impure gaseous nitrogen containing impurities at least of the O2 type by putting the impure nitrogen in contact with a catalyst and then with a molecular sieve mixing the pure nitrogen obtained with nitric oxide (NO), and obtaining a mixture formed from NO and pure nitrogen containing an NO content of less than 20% by volume and a proportion of impurities of the O2 type of less than 5 ppmv and of the H2O type of less than 40 ppmv. The NO/nitrogen mixture may undergo supplementary dilutions with pure nitrogen. Such NO/nitrogen mixtures can be used for treating, by inhalation, pulmonary vasoconstrictions in adults or children, in particular in new-born babies suffering from primitive pulmonary hypertension or in patients undergoing heart surgery.
