1. Glycosaminoglycans were liberated from old and young human ascending aortae by digestion with papain. Heparan sulphate and chondroitin sulphate were separated by the different solubilities of their complexes with cetylpyridinium chloride in solutions of sodium chloride. Final fractionation was achieved by salt-gradient column chromatography on Dowex 1 (Cl(-)form). 2. Heparan sulphate from old aortae showed a slight, but consistent, increase in sulphation compared with heparan sulphate from young aortae. 3. The major amino acids associated with aortic heparan sulphate and chondroitin sulphate were serine, glycine, glutamic acid and aspartic acid. Heparan sulphate and chondroitin sulphate from old aortae contained about twice as much total amino acid as heparan sulphate and chondroitin sulphate from young aortae. Alkali hydrolysis resulted in the destruction of more serine in chondroitin sulphate from old, compared with young, aortae. 4. Molecular weights of glycosaminoglycans from old and young aortae were found to be similar, and in the region of 35000. 5. It is suggested that there is an increased degree of protein-glycosaminoglycan cross-linking in old aortae.