The treatment of wheat straw with 2% H2O2 at 50 degrees C and pH 11.5 for 4-30 h or with 2% H2O2-0.05% anthraquinone at 50 degrees C and pH 11.5 for 4.5 h resulted in the release of 79-86% of the original lignin and 77-91% of the original hemicelluloses, which contained 3.8-6.5% of associated lignins. Xylose was the major sugar constituent in all the solubilized hemicellulosic fractions, and arabinose, glucose, and galactose were present in small amounts. The isolated seven hemicellulosic samples were further characterized by Fourier transform infrared, and carbon-13 magnetic resonance spectroscopy as well as gel permeation chromatography. Comparison of these hemicellulosic fractions with those obtained by alkali extraction from wheat straw in the absence of hydrogen peroxide provided evidence of similar chemical composition and structure. The treatment by alkaline peroxide under the conditions used did not result in any significant change in the macromolecular structure of hemicelluloses.