The pentasaccharide (XXG), Xyl Xyl ↓ ↓ Glc → Glc → Glc obtained from Rosa xyloglucan, was converted to two isomeric tetrasaccharides, a and b (Xyl 1 Glc 3 ), by mild acid hydrolysis. During hydrolysis in 2 M trifluoroacetic acid at 90°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 andb yielded cellobiose and Xyl → Glc → Glc, respectively, showing that they were Xyl Xyl ↓ ↓ Glc → Glc → Glc and Glc → Glc → Glc, respectively. Tetrasaccharide b was chromatographically identical, upon HPLC on Dionex CarboPac PA1, with the tetrasaccharide produced from XXG by the action of Tropaeolum α-d-xylosidase, supporting the proposed structure. Xyloglucan oligosaccharides were assayed quantitatively by measurement of the yield of isoprimeverose (Xyl → Glc) after complete Driselase digestion.