Culture of chondrocytes in the presence of 4-methylumbelliferyl beta-D-xyloside resulted in a synthesis of protein-free, fluorogenic chondroitin sulfate which was heterogeneous on DEAE-cellulose chromatography. Degradation of the major chromatographic fraction with chondroitinase-ABC yielded, in addition to a large quantity of delta4-glucuronic acid-containing disaccharides, two fluorogenic oligosaccharides of different size. Quantitative analysis showed that delta4-glucuronic acid, galactose, xylose, and 4-methylumbelliferone were present in the small oligosaccharide fragment in a molar ratio of 1:2:1:1. Since these analytical data are analogous to those reported for glycopeptides derivedfrom proteochondroitin sulfates, it may be suggested that 4-methyl-umbelliferyl beta-D-xyloside replaces the need for xylosyl protein core in the normal synthesis of proteochondroitin sulfate with a resultant production of the unusual polysaccharide bearing the added xyloside at the reducing end.