The seeds of Ipomoea fistulosa contain a water-soluble galactomannan composed of residues of D-galactose and D-mannose in the ratio 3 : 10. Hydrolysis of the methylated polysaccharide gave 2,3,4,6-tetra-O-methyl-D-mannose (3 mol), 2,3,6-tri-O-methyl-D-mannose (7 mol), and 2,3-di-O-methyl-D-mannose (3 mol). Periodate oxidation data indicated 22.1 % of end groups, and methylation 22.8 %. The above findings, together with data on the oligosaccharides formed on partial hydrolysis with acid, showed the galactomannan to consist of a linear chain of (1→4)-linked β-D-mannosyl residues to which α-D-galactosyl groups are attached by (1→6) linkages.