The native proteoheteroglycan (PHG) from mycelia of Neurospora crassa contain two kinds of carbohydrate chains differing structure. The oligosaccharides containing mannose and galactofuranose are attached by O-glycosidic linkages to serine or threonine residues in the protein (J. Biochem. 96, 1005-1011, 1984). The second kind of carbohydrate chain is a polysaccharide containing mannose and galactofuranose as the main sugar components. The results of structural studies with methylation and NMR analyses on the native PHG and some of its specifically degraded products obtained on partial acid hydrolysis and acetolysis indicate that the polysaccharide moiety of the PHG has an (alpha 1-6) linked mannan backbone with mainly (alpha 1-2) linked side chains, each of which consists of 2 to 5 mannose units, and most of the mannosyl side chains bear beta-galactofuranosyl residues linked to the 2 positions of the mannosyl nonreducing terminals. The galactofuranose residues are linked with each other by (beta 1-5) bonds.