Two halanaerobic bacteria--Halanaerobium saccharolytica subsp. senegalense and Halanaerobium sp. strain FR1H--produced acetate, H2, and CO2 from glycerol fermentation, but the glycerol consumption rate was low. In contrast, in the presence of the moderately halophilic hydrogenotrophic sulfate-reducing bacterium, Desulfohalobium retbaense, used as H2 scavenger in the coculture, glycerol oxidation by both halanaerobes significantly increased. Cocultures of both halanaerobes with D. retbaense on glycerol led to acetate, hydrogen sulfide, and CO2 production, whereas glycerol fermentation by the two strains led to the production of acetate, hydrogen, and CO2. The increased glycerol oxidation by H. saccharolytica and strain FRI H in coculture with D. retbaense resulted from low H2 partial pressure caused by the hydrogen-oxidizing activity of D. retbaense. These results provide the first evidence of interspecies hydrogen transfer in saline environments and indicate that this mechanism may play an important role in organic matter mineralization in hypersaline ecosystems.