A polysaccharide, isolated from rapeseed hulls by extraction with aqueous sodium hydroxide-sodium tetraborate, contained residues of L-arabinose, L-fucose, D-xylose, D-galactose, and D-glucose in the proportions of 2:8:25:13:52. Acetolysis furnished cellobiose, 6-O-alpha-D-xylopyranosyl-D-glucose, and 2-O-beta-D-galactopyranosyl D-xylose. The cleavage products from the methylated polysaccharide were examined by g.l.c. of the methyl glycosides and g.l.c.-mass spectrometry of the partially methylated, alditol acetates. The results show that the polysaccharide is a member of the xyloglucan group in which additional fucose and galactose residues terminate some of the side-chains. For comparative purposes, aspects of the structures of xyloglucans from nasturtium seeds and suspension-cultured sycamore cells have been re-examined.