Objective To explore the change of serum osteopontin concentration and the expression of OPN in the synovial membrane of patients with rheumatoid arthritis.Methods We measured the serum osteo-pontin concentration in 91 RA patients and 29 sex-and age-matched normal control subjects using an en-zyme-linked immunoabsorbent assay and collected clinic data at the same time.The expression of OPN in the synovial membrane from 7 RA patients and 1 patient with trauma was examined by immunohistochemisty.Results Serum osteopontin concentrations were significantly higher in both active and inactive RA patients than that in the normal control group:(65±22)ng/ml in active RA,(56±22)ng/ml in inactive RA patients and(26±8)ng/ml(P＜0.005)in normal controls.Increase in OPN concentration correlated positively and sig-nificantly with the number of tender joints,joint x-ray change stages,and joint function(r=O.435,P=0.005.r=0.415,P=0.007,r=O.394,PP=0.012).The expression of OPN was observed in all samples from patients.OPN was expressed in the synovial lining and sublining layer.Conclusion The above results suggest that the pro-duction of osteopontin is associated with joint destruction in RA.