We have investigated H-2 production on glucose, xylose, arabinose, and glycerol in Thermotoga maritima and T. neapolitana. Both species metabolised all sugars with hydrogen yields of 2.7-3.8 mol mol(-1) sugar. Both pentoses were at least comparable to glucose with respect to their qualities as substrates for hydrogen production, while glycerol was not metabolised by either species. Glycerol was also not metabolised by T. elfii. We also demonstrated that T. neapolitana can use wet oxidised wheat straws, in which most sugars are stored in glycoside polymers, for growth and efficient hydrogen production, while glucose, xylose and arabinose are consumed in parallel.