Glucose and xylose are the dominant monomeric carbohydrates present in agricultural materials which can be used as potential building blocks for various biotechnological products including biofuels production Hence, the imperative role of glucose to xylose ratio on fermentative biohydrogen production by mixed anaerobic consortia was investigated. Microbial catabolic H(2) and VFA production studies revealed that xylose is a preferred carbon source compared to glucose when used individually. A maximum of 1550 and 1650 ml of cumulative H(2) production was observed with supplementation of glucose and xylose at a concentration of 5.5 and 5 0 g L(-1), respectively. A triphasic pattern of H(2) production was observed only with studied xylose concentration range pH impact data revealed effective H(2) production at pH 6.0 and 6 5 with xylose and glucose as carbon sources, respectively. Co-substrate related biohydrogen fermentation studies indicated that glucose to xylose ratio influence H(2) and as well as VFA production. An optimum cumulative H(2) production of 1900 ml for 5 g L(-1) substrate was noticed with fermentation medium supplemented with glucose to xylose ratio of 2:3 at pH 6 Overall, biohydrogen producing microbial consortia developed from buffalo dung could be more effective for H(2) production from lignocellulosic hydrolysates however, maintenance of glucose to xylose ratio, inoculum concentration and medium pH would be essential requirements. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved