The wet oxidation process (water, oxygen, elevated temperature, sodium carbonate) was investigated as a means of solubilising hemicellulose from wheat straw. Sixteen different combinations of oxygen pressure and sodium carbonate concentration were applied. The hemicellulose hydrolysates were evaluated with respect to total sugars, xylose, and 2-furfural produced. The concentration of sugars tended to be highest in hydrolysates produced at high oxygen pressures, whereas the concentration of 2-furfural was lowest in hydrolysates produced at low oxygen pressures and high carbonate concentrations. Fermentation of the hydrolysates was carried out using Thermoanaerobacter mathranii strain A3M1. No significant inhibitory effect was observed when the hydrolysates were fermented by T. mathranii A3M1. However, the solubilised hemicellulose was only partly available for fermentation by the bacteria. Treatment with the commercial enzyme Celluclast(R) or with acid hydrolysis improved the ethanol yield from the hydrolysates. Treatment with Pentopan(TH) Mono BG or Pulpzyme(R) HC, both endo-1,4-beta-xylanases, had no effect neither had co-cultivation with the xylanase-producing Dictyoglomus B4. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.