The pentasaccharide (XXG), [formula: see text] obtained from Rosa xyloglucan, was converted to two isomeric tetrasaccharides, a and b (Xyl1.Glc3), by mild acid hydrolysis. During hydrolysis in 2 M trifluoroacetic acid at 90 degrees C, optimal yields of a and b were obtained after 20-40 min. Each tetrasaccharide was purified by preparative paper chromatography and high-pressure liquid chromatography (HPLC). The two isomers were distinguished by the products of their partial digestion with Driselase, which hydrolyses the glucosidic bonds sequentially from the non-reducing terminus: a and b yielded cellobiose and Xyl-->Glc-->Glc, respectively showing that they were [formula: see text] and [formula: see text] respectively. Tetrasaccharide b was chromatographically identical, upon HPLC on Dionex CarboPac PA1, with the tetrasaccharide produced from XXG by the action of Tropaeolum alpha-D-xylosidase, supporting the proposed structure. Xyloglucan oligosaccharides were assayed quantitatively by measurement of the yield of isoprimeverose (Xyl-->Glc) after complete Driselase digestion.