['To investigate whether fragmentation of proteoglycans in arthritis results in domains that have different levels of release from cartilage at different stages of the disease.', 'Two regions of the proteoglycan, the hyaluronan-binding region and the glycosaminoglycan-rich region of the core protein, were measured, by immunoassay, in knee joint synovial fluids of patients with rheumatoid arthritis or reactive arthritis.', 'Synovial fluid concentrations of the glycosaminoglycan-rich region were highest in rheumatoid arthritis patients who had little cartilage damage as determined by radiography, whereas release of the hyaluronan-binding region predominated in patients with advanced cartilage destruction. In reactive arthritis, release of the glycosaminoglycan-rich region predominated.'] Does synovial fluid analysis of two groups of proteoglycan epitopes distinguish early and late cartilage lesions?