Fermentations can be used to produce sustainable energy carriers, such as hydrogen and ethanol (EtOH), from biomass or organic waste materials. The aim of this research was to prospect efficient H-2- and EtOH-producing thermophilic microorganisms derived from hot spring environments in Iceland. Hydrogen- and EtOH-producing enrichment cultures were obtained from various hot spring samples over a temperature range of 50 - 78 degrees C. The temperature dependencies for the most promising enrichments were determined with a temperature-gradient incubator. One of the enrichments (33HL) produced 2.10 mol of H-2/mol of glucose at 59 degrees C. Another enrichment (9HG), dominated by bacteria closely affiliated with Thermoanaerobacter thermohydrosulfuricus, produced 0.68 mol of H-2/mol of glucose, and 1.21 mol of EtOH/mol of glucose at 78 degrees C. Hydrogen and EtOH production by 9HG was characterized further in a continuous-flow bioreactor at 74 degrees C. The highest H-2 and EtOH yields of 9HG were obtained at pH 6.8 +/- 0.3. Lactate production decreased the H-2 and EtOH yields in the continuous-flow bioreactor, and the yields were lower than those obtained in the batch fermentations. In conclusion, the thorough batch screening, of Icelandic hot spring samples indicated some promising enrichments for H-2 or H-2 plus EtOH production from carbohydrate materials.