Semicontinuous anaerobic digestion of cattle dung using brackish waters with conductivity from 1000-15000 mu S/cm was carried out in 25 l biogas plants of floating-dome design. Water with a conductivity higher than 5000 mu S/cm was inhibitory to the process. Experiments using three cultures of methanogens: Methanobacterium bryantii Methanobacterium formicicum and Methanosarcina barkeri confirmed these findings. Methanobacterium bryantii was found to tolerate water of the highest conductivity. Copyright (C) 1997 Elsevier Science Ltd.