Proteoglycan subunits (PGS) were isolated from bovine articular cartilage of calves and from cows, 18 months and 8 years old respectively. From the latter cartilage of osteoarthrotic and of non-osteoarthrotic sites was taken. PGS were characterized by gel-chromatography on Sepharose 2B columns and subjected to digestion with chondroitinase ABC and with papain. The isolated keratan sulphate-protein cores obtained from chondroitinase digestion were characterized on Sepharose 4B and the chondroitin sulphate chains on Sephadex G-200 gels. A larger molecular size of PGS was found in calf cartilage than in the other samples. This was attributed to the larger molecular size of chondroitin, whereas no change was observed in the keratan sulphate-protein cores. No change was observed in molecular size of PGS, isolated chondroitin sulphates or keratan sulphate-protein cores in osteoarthrosis in compariith non-osteoarthrotic cartilage from the same joint or from younger adult animals.