The polysaccharide has been purified; after nitric acid oxidation small quantities of mucio and saccharic acids have been obtained. The carbohydrate has been methylated by repeated treatment with Me2SO4, NaOH the chloroform soluble fraction being further methylated with Mel Ag2O to a product with OMe, 31% Prior treatments to give an acelylated product or sulphate free product, suitable for methylation, were unsuccessful. The properties of fully methylated and CHCI3 insoluble fractions have been investigated; the former fraction was subjected to methanolysis and the products separated and investigated. Evidence for 2:3:4-trimethyl-L-rhamnose and no other simple end group, partially methylated hexose and rhamnose an anhydro structure and an ester was obtained. On autohydrolysis most of the aronic acid and/or pentose is hydrolysed with about 50% of the rhamnose, leaving an unstable macromolecular residue.