The carbonyl content of proteins in the synovial fluid (SF) of patients with rheumatoid arthritis was significantly (p less than or equal to 0.10) elevated over levels in the SF of patients with osteoarthritis (OA). Other indicators of oxidative damage including catalse, ceruloplasmin, ferritin and superoxide dismutase also showed statistically significant differences (p less than or equal to 0.05) compared to patients with OA.