The alkali-extractable water-soluble polysaccharides F1SS isolated from the cell wall of four species of Discula destructiva have been studied by methylation analysis and NMR spectroscopy, and their idealized structures established as [structure: see text] where n approximately 2 for strains CBS 109771 and CBS 133.91, n approximately 1 for CBS 132.91, and it has an intermediate value in strain CBS 130.91. The mannan core was obtained by mild hydrolysis of the F1SS polysaccharide and its structure consisted of a skeleton of alpha-(1-->6)-mannopyranan, with around one out of eleven residues substituted at C-2 by short chains (one to six units) of 2-substituted mannopyranoses.