In this study, positive correlations were found between tumor necrosis factor alpha (TNF alpha) levels in the sera of rheumatoid arthritis (RA) patients and the duration of morning stiffness, joint tenderness count, the Ritchie articular index and erythrocyte sedimentation rate. Further, higher mean grades of disease activity of RA were accompanied by correspondingly higher levels of serum and synovial TNF alpha. In the longitudinal study, when the disease activity of RA decreased after treatment, serum TNF alpha levels also decreased. This suggests that the levels of serum and synovial TNF alpha correlate positively with RA disease activity. The levels of TNF alpha in synovial fluid were significantly higher in RA and acute gouty arthritis (GA) patients than in osteoarthritis (OA) patients. This suggests that joint inflammation in inflammatory arthritis related to local production of TNF alpha in the joint cavities. Serum TNF alpha levels in RA patients were significantly higher than those in the OA patients; no statistical difference was found between acute GA and OA patients.