A stable anoxic enrichment culture was obtained that degraded benzene with chlorate as an electron acceptor. The benzene degradation rate was 1.65 mM benzene per day, which is similar to reported aerobic benzene degradation rates but 20-1650 times higher than reported for anaerobic benzene degradation. Denaturing gradient gel electrophoresis of part of the 16S rRNA gene, cloning and sequencing showed that the culture had a stable composition after the seventh transfer. Five bacterial clones were further analyzed. Two clones corresponded to bacteria closely related to Alicycliphilus denitrificans K601. The three other clones corresponded to bacteria closely related to Zoogloea resiniphila PIV-3A2w, Mesorhizobium sp. WG and Stenotrophomonas acidaminiphila. DGGE analysis of cultures grown with different electron donors and acceptors indicated that the bacterium related to Alicycliphilus denitrificans K601 is able to degrade benzene coupled to chlorate reduction. The role of the other bacteria could not be conclusively determined. The bacterium related to Mesorhizobium sp. WG can be enriched with benzene and oxygen, but not with acetate and chlorate, while the bacterium related to Stenotrophomonas acidaminophila grows with acetate and chlorate, but not with benzene and oxygen. As oxygen is produced during chlorate reduction, an aerobic pathway of benzene degradation is most likely. © 2007 Federation of European Microbiological Societies.