Preparation of aromatic or heteroaromatic nitrites of the formula I ##STR1## where X is nitrogen or C-R.sup.6 and all of the R substituents represent hydrogen, alkyl, halogen, nitro, amino or similar groups, provided at least one substituent is a cyano or alkylcyano group. The nitrites I are produced by reacting aromatic or heteroaromatic hydrocarbons of the formula II ##STR2## where X is nitrogen or C-R.sup.6, provided at least one substituent is C.sub.1 -C.sub.8 -alkyl, with ammonia and oxygen at 200 to 600.degree. C. under a pressure of 0.1 to 5 bar in the gas phase over a supported catalyst containing 0.5 to 20% by weight of vanadium oxide. The supported catalyst consists of from 2 to 30 particle fractions whose mean diameters differ by from 10 to 80% and the supporting carrier of the catalyst has a bulk density of 0.6 to 1.2 kg/liter.