The potential for degradation of four nitrogen-heterocyclic compounds was investigated in freshwater sediment slurries maintained under denitrifying, sulfate-reducing and methanogenic conditions. Pyridine (10 mg/1) was rapidly transformed within 4 weeks under denitrifying conditions but persisted for up to 3 months under sulfate-reducing and methanogenic conditions. Quinoline (10 mg/1) was completely transformed without a lag phase under methanogenic and sulfate-reducing conditions after incubation for 23 and 45 days, respectively. Under denitrifying conditions, less than 23% of the initial concentration of quinoline was transformed after anaerobic incubation for 83 days. Indole, however, was completely removed from sediment slurries under denitrifying, sulfate-reducing, and methanogenic conditions after anaerobic incubation for 18, 27, and 17 days, respectively. No evidence for biotransformation of carbazole was noted for all anaerobic conditions tested.