Treatment of wood with chromic acid and other hexavalent chromium compounds has been shown to improve surface characteristics. Most trivalent chromium compounds do not become fixed in wood (i.e., do not form water-insoluble wood-chemical complexes). However, chromium (III) nitrate treatment of western red cedar (<i>thuja plicata</i>), southern pine, and ponderosa pine produced modified wood with properties similar to chromic acid-treated wood. Evaluation of the chromium (III) nitrate-and chromic acid-modified wood by leaching, Xenon arc-accelerated weathering, and swellometer experiments clearly demonstrated similar fixation, erosion, and water-repellent properties. Based on the results from chromium (III) nitrate-treated wood, fixation through coordination of trivalent chromium with wood hydroxyl and formation of insoluble chromium appear to be the critical factors in improving the performance of the treated wood. Thus, the oxidation of the wood surface by hexavalent chromium appears to be less important and may not be required for improving properties. -- AATA