Air-dried samples of sweet sorghum, sugarcane bagasse, wheat straw, maize leaves and silphium were utilized without chemical pretreatment as sole energy and carbon sources for H(2) production by the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus. The specific H(2) production rates and yields were determined in the batch fermentation process. The best substrate was wheat straw, with H(2) production capacity of 44.7 L H(2) (kg dry biomass)(-1) and H(2) yield of 3.8 mol H(2) (mol glucose)(-1). Enzymatically pretreated maize leaves exhibited H(2) production of 38 L H(2) (kg dry biomass)(-1). Slightly less H(2) was obtained from homogenized whole plants of sweet sorghum. Sweet sorghum juice was an excellent H(2) source. Silphium trifoliatum was also fermented though with a moderate production. The results showed that drying is a good storage method and raw plant biomass can be utilized efficiently for thermophilic H(2) production. The data were critically compared with recently published observations. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.