A constructed microbial consortium was formulated from three facultative H-2-producing anaerobic bacteria, Enterobacter cloacae IIT-BT 08, Citrobacter freundii IIT-BT L139 and Bacillus coagulans IIT-BT Si. This consortium was tested as the seed culture for H-2 production. In the initial studies with defined medium (MYG), E. cloacae produced more H-2 than the other two strains and it also was found to be the dominant member when consortium was used. On the other hand, B. coagulans as a pure culture gave better H-2 yield (37.16 ml H-2/g CODconsumed) than the other two strains using sewage sludge as substrate. The pretreatment of sludge included sterilization (15% v/v), dilution and supplementation with 0.5% w/v glucose, which was found to be essential to screen out the H-2 consuming bacteria and ameliorate the H-2 production. Considering (1:1:1) defined consortium as inoculum, COD reduction was higher and yield of H-2 was recorded to be 41.23 ml H-2/g CODreduced. Microbial profiling of the spent sludge showed that B. coagulans was the dominant member in the constructed consortium contributing towards H-2 production. Increase in H-2 yield indicated that in consortium, the substrate utilization was significantly higher. The H-2 yield from pretreated sludge (35.54 ml H-2/g sludge) was comparatively higher than that reported in literature (8.1-16.9 ml H-2/g sludge). Employing formulated microbial consortium for biohydrogen production is a successful attempt to augment the H-2 yield from sewage sludge. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.