Cytokine-specific monoclonal antibodies were used in enzyme-linked immunoadsorbant assays (ELISA) to examine a variety of synovial fluids for the presence of cytokines which might be expected to play some part in the pathology of arthritis. Low, but significant, levels of tumour necrosis factor alpha (TNF-alpha) were present in the majority of synovial fluids obtained from rheumatoid arthritis patients with a sero-positive history. Low levels of interferon (IFN)-alpha and IFN-gamma were also detected, but only IFN-alpha was significantly increased in the sero-positive group. Tumour necrosis factor beta (TNF-beta) was present only in trace amounts. These results suggest that the presence of cytokines, such as TNF-alpha and IFN-alpha in synovial fluid may be associated with tissue changes observed in rheumatoid joint disease and thus contribute to the pathology of the arthritis, but support evidence for the minimal role likely to be played by IFN-gamma in the joint pathology of rheumatoid arthritis.