Sulfurospirillum multivorans and Desulfitobacterium hafniense PCE-S are anaerobes that can utilize tetrachloroethene (PCE) as an electron acceptor in their energy metabolism. The end-product of PCE reduction for both organisms is cis-1,2-dichloroethene, which is formed via trichloroethene as the intermediate. The bacteria were able to dehalogenate cis- and trans-1,2-dibromoethene (cDBE and tDBE) in growing cultures and cell extracts. Dibromoethene supported growth of both organisms. The organisms debrominated cDBE and tDBE to vinyl bromide (VB); D. hafniense PCE-S also produced ethene in addition to VB. The PCE reductive dehalogenases (PCE dehalogenases) of S. multivorans and D. hafniense PCE-S mediated the debromination of tribromoethene (TBE) and both isomers of 1,2-DBE, indicating that this enzyme was responsible for the reductive dehalogenation of brominated ethenes. cDBE, tDBE, 1,1-DBE and VB were formed upon TBE debromination; VB was the major end-product. The PCE dehalogenase of D. hafniense PCE-S also formed ethene. With the purified enzymes from both organisms the kinetic properties of dehalogenation of brominated alkenes were studied and compared with those of their chlorinated analogues.