The bacterial community structure of anaerobic enrichment cultures that are capable of degrading both cis-1,2-dichloroethylene (cis-DCE) and vinyl chloride (VC) and isolation of the organism responsible for the degradation were investigated. Denaturing gradient gel electrophoresis (DGGE) of a PCR-amplified 16S rRNA gene from the cultures showed the possible predominance of Clostridium species. One isolate, designated strain DC1, was closely related to members of Clostridiaceae, based on 16S rRNA gene analysis, and the highest sequence similarity (98.9%) was obtained for Clostridium saccarobutylicum. In culture experiments, strain DC1 was shown to degrade cis-DCE and VC during the stationary phase of growth without accumulation of VC and/or ethene. The bacterial growth was not linked to the degradation of cis-DCE and VC. Stoichiometric analysis revealed that two moles of chloride ions as released from one mole of cis-DCE during the incubation period, indicating that cis-DCE was fully dechlorinated. The results appear consistent with the presence of a mechanism of oxidative dechlorination rather than respiratory reductive dechlorination; the latter is accompanied by transient formation of dechlorinated ethenes from cis-DCE and VC.