The metabolic fate of 2-hydroxybiphenyl under different anaerobic conditions was tested with sediment slurries and enrichment cultures obtained from a shallow anoxic aquifer. 2-Hydroxybiphenyl was depleted in aquifer slurries over the course of incubation, but substrate loss in methanogenic slurries was not significantly different from either filter-sterilized or autoclaved controls. In contrast, the rate of substrate removal was significantly higher in non-sterile, sulfate-reducing aquifer slurries relative to abiotic control incubations. A 2-hydroxybiphenyl-degrading enrichment was established that was inhibited by molybdate but not by bromoethanesulfonic acid. For every mole of substrate consumed by the bacterial consortium, 6.1 +/- 0.2 moles of sulfate were depleted from the enrichment medium. This represents about 87% of the theoretical amount of sulfate consumed and suggests that the 2-hydroxybiphenyl was largely mineralized. Oxygen, nitrate, or carbon dioxide could not replace sulfate as a terminal electron acceptor for the enrichment. Other hydroxybiphenyl isomers were not metabolized by these cultures. This study shows that aromatic substrates with multiple ring systems can undergo biotransformation by anaerobic microorganisms under some ecological conditions.