Strain DCB-1 is a strict anaerobe capable of the reductive dechlorination of chlorobenzoates. The effect of dechlorination on the yield of pure cultures od DCB-1 was tested. Cultures were incubated with formate or H2 as electron donors and CO2 as a putative carbon source. Relative to control cultures with benzoate, cultures which dechlorinated 3-chlorobenzoate and 3,5-dichlorobenzoate had higher yields measured both as protein and cell density. On the media tested the apparent growth yield was 1.7 to 3.4 g cell protein per mole Cl- removed. Dechlorination also stimulated formate oxidation by growing cultures. Resuspended cells required an electron donor for dechlorination activity, with either formate or elemental iron serving this function. Resuspended cells did not require an electron acceptor for formate consumption, but reductive dechlorination of 3CB to benzoate stoichiometrically stimulated oxidation of formate to CO2. These results indicate that DCB-1 conserves energy for growth by coupling formate, and probably, H2 oxidation to reductive dechlorination.