When the articular cartilage slices of new born calf were incubated in the presence of xanthine oxidase and hypoxanthine, an oxygen radical generating system, the degradation of cartilage proteoglycan was increased significantly. This effect was not inhibited by superoxide dismutase or diethylenetriaminepentaacetic acid,but was inhibited by catalase. Addition of H2O2 to the incubation medium also enhanced the proteoglycan degradation of articular cartilage, and this effect was promoted significantly by Cu2+ or Co2+. Analyses of the degradation products of cartilage proteoglycan on Sepharose 6B chromatography showed one macromolecular peak at kD = 0 in many of the experimental groups, but there were two peaks at kD = 0 and 0.57(peak �� and peak �� respectively) in the H2O2 + Cu2+ group.Two-dimensional electrophoresis on cellulose acetate membrane confirmed that the peak �� was cho-ndroitin sulphate, it means that the complex of Cu2+ and H2O2 would lead to the breakage of proteoglycan molecules. These results might be helpful in understanding the pathogenesis of some degenerative joint diseases, such as Kashin-Beck disease related to selenium deficiency.