Without oxidizing reagents or catalysts, ethanol was smoothly converted to CH(3)CHO and H(2) in supercritical water at 450-500degreesC. CH(3)CHO was further decomposed into CH(4) and CO instead of being oxidized into acetic acid. These features suggest the direct participation of water molecules in the ethanol dehydrogenation. (C) 2003 Elsevier Science Ltd. All rights reserved.