Summary:We investigated the diagnostic significance of UDP-Z>-xylose: proteoglycan core protein ß-£>-xylosyltransferase (EC 2.4.2.26) in different chronic joint diseases. This eiizyme is located almost exclusively within chondrocytes, where it initiales the formation of chondroitin sulphate during the biosynthesis of proteoglycans and from which it is easily released after damage of articular cartilage.