Reductive dechlorination of tetrachloroethene (PCE) was investigated in two anaerobic bacteria which belong to different phylogenetic groups. The PCE dehalogenases of both bacteria are able to degrade PCE to cis-1,2-dichloroethene. Dehalospirillum multivorans (gram-) is able to grow with hydrogen and PCE as sole energy sources. The energy is gained by a new type of anaerobic respiration with PCE as terminal electron acceptor. The electron transport chain probably involves a reversed electron flow. The PCE dehalogenase of Desulfitobacterium strain PCE-S (gram+) was purified and characterized. The enzym contains 1 corrinoid and 2 Fe/S-clusters. The corrinoid is necessary for the transformation of PCE and is involved in a redox-reaction, which is unique for corrinoid-dependent enzymes.