The characteristics of H(2) production by anaerobic mixed microflora in a submerged membrane bioreactor (MBR) were investigated. For comparative purposes, a continuous stirred tank reactor (CSTR) was operated in parallel under the same conditions. The experimental results showed that 35-day stable and continuous H2 fermentation was successfully achieved, the MBR revealing an H2 content of 51% and the CSTR, 58%. No methane gas was detected during the experiments for the long solids retention time (SRT) of 90 days. The MBR's H2 production rate was 2.43-2.56 l H(2) l(-1) d(-1), which was about 2.6 times higher than that (0.95-0.971 H(2) l(-1) d(-1)) of the CSTR, reflecting the MBR's higher H(2) productivity. (C) 2008 Elsevier Ltd. All rights reserved.