Alkali hydrothermal experiments with glycolaldehyde were carried out at 300 degrees C. Glycolaldehyde was converted into lactic acid in a yield of 28% based on the starting carbon mass of glycolaldehyde. A conversion pathway for glycolaidehyde into lactic acid is proposed and our results suggest that the pathway via glycolaldehyde is also important in the conversion of glucose into lactic acid. (c) 2006 Elsevier Ltd. All rights reserved.