The presence of neutrophils in the synovial joint of patients with rheumatoid arthritis (RA) is thought to be due to the activity of chemotactic factors released by activated cells in the joint. We have shown in this report, for the first time, the abundance of one such factor, interleukin 8 (IL 8), in the synovial fluid of patients both with RA and other non‐RA joint diseases, and the spontaneous production of IL8 mRNA by RA synovial cells in culture. There was no correlation between the levels of chemotactic activity and IL8 protein, suggesting that other factors with similar neutrophil chemotactic activity are also present in the synovial fluid exudate. In support of this concept neither the level of chemotactic activity nor IL8 protein levels correlated with neutrophil or leukocyte infiltration, indicating that the mechanism of migration into the inflammatory environment of the joint is complex. Such migration is likely to be due to a number of chemotactic signals in addition to IL8, which may either synergize with, or inhibit, the action of IL8.