Heterocyclic polyaromatic compounds, including dinaphthofurans, 2-(2-naphthalenyl)benzothiophene, methylated chrysene, and benz[a]anthracene, were identified and confirmed as major cytochrome P4501A (CYP1A)-inducing compounds in a contaminated sediment close to the industrial site of Bitterfeld (Germany). Identification was achieved by the application of an effect-directed fractionation and analysis approach. This approach comprised the combination of a rainbow trout liver cell line (RTL-W1) bioassay to select for CYP1A-inducing effects by measuring 7-ethoxyresorufin-O-deethylase activity, a multistep fractionation procedure, and various methods Of Chemical characterization. The identified nonpriority pollutants were found to be significantly more potent than the reference compound, benzo[a]pyrene, and among the most potent polycyclic inducers known. On the basis of the history of industrial activity at the contaminated site, the heterocyclic compounds identified in this study are thought to stem from 2-naphthol production. 2-Naphthol is one of the most high tonnage products of the aniline dye industry in general, thereby indicating the potential environmental relevance of the identified heterocyclic aromatic compounds. To date, however, no or very little knowledge exists about their occurrence, fate, and biological effects.