A simplified and relatively rapid method, based on a gas chromatographic determination preceded by a thin-layer chromatography, for the separation of heterocyclic nitrogen compounds in atmospheric particulate matter has been developed. The benzene extract of the dust is applied to a silanized silica gel plate and developed with benzene-hexane-pyridine(4:5:1). In this way, aza-heterocyclic compounds are separated from other classes of components, such as polynuclear hydrocarbons and paraffins. The portion containing aza-heterocyclic compounds is extracted again and examined by gas chromatography on a high-efficiency glass capillary column coated with Versamid 900.