Aromatic hydrocarbons have long been recognized as ubiquitous pollutants in our environment. It is in general very difficult or even impossible to establish the origin of these compounds. On the one hand their source may be spills of fossil fuels or fallout of incompletely combusted organic material. On the other hand they are widely used as organic intermediates and solvents in trade and industry. The analytical methods for this class of compounds are discussed. A method based on a combined system of gas chromatography and mass spectrometry is described in detail. The data handling is performed by an on-line coupled, dedicated computer. Three examples (domestic sewage, diesel fuel, and oil contaminated recent sediment) show the feasibility of the method. An extensive characterization of the aromatic hydrocarbon mixtures in sewage and sediment samples permits conclusions about their origin.