Attempts to characterize the breakdown product formed during the anaerobic degradation of the gamma isomer of benzene hexachloride (γ-BHC, C6H6Cl6) by the Clostridium sp. were made. Analysis by gas chromatography and thin-layer chromatography indicated that the degradation product of γ-BHC and α-BHC differed from γ-pentachlorocyclohexene (C6H5Cl5), a direct product of dehydrochlorination of γ-BHC. The ability of the bacterium to convert DDT to DDD by reductive dechlorination suggested that a similar mechanism might degrade γ-BHC to γ-pentachlorocyclohexane (C6H7Cl5). Potassium nitrate inhibited the bacterial degradation of γ-BHC whereas potassium sulfate and potassium chloride enhanced it.