Background/Aim. Many arguments prove the pathophysiologic role of histamine in the process of remodeling and joint destruction in rheumatoid arthritis. The aim of our study was to find out if there was a relation between histamine concentration in synovial fluid and blood with clinical expression of disease activity. Methods. Histamine concentration in synovial fluid and blood was determinated in 19 patients with rheumatoid arthritis. Histamine concentration measurement was based on the Shore's fluorometric method. Histamine index (HI) was evaluated as a ratio between histamine concentration in synovial fluid and blood. Disease activity score, DAS 28 (3), with three variables (erythrocyte sedimentation rate, the number of swelled joints and the number of tender joints) was also evaluated. Results. Our results showed that there was no significant difference in concentration of histamine in synovial fluid and blood related to disease activity. However, there was a significant difference in the histamine index which was increased proportionally with disease activity. Conclusion. Our study indicates that histamine index could be useful in estimation of rheumatoid arthritis activity.