Using a synthetic medium supplemented with biphenyl (a polycyclic aromatic hydrocarbon), a new bacterial strain of Citrobacter freundii was isolated from enrichment cultures containing soil and industrial wastewater samples of the Serpukhov Condenser Factory. This strain was found to be capable of degrading biphenyl under anaerobic conditions in the course of nitrate reduction. When the initial concentration of biphenyl in culture medium equaled 150 mg/l, the culture with a titer of 10(9) cells/ml degraded up to 26-28% of biphenyl in 3 days (28 degrees C). At 250 mg/l, the culture with a titer of 10(7) cells/ml degraded 15% of biphenyl in 21 days. Approximately 10% of the substrate consumed was utilized completely, whereas the remainder underwent transformation.