We used a newly developed, sensitive ELISPOT technique in order to estimate the number of cells producing interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) in synovial fluid mononuclear cells (SFMC) and peripheral blood mononuclear cells (PBMC) in patients with rheumatoid arthritis (RA) and other inflammatory arthritides, and to correlate the results with clinical and laboratory parameters of disease activity. SFMC and PBMC were cultured either without stimuli or with a standardized dose of phytohaemagglutinin (PHA) for 6 h. Twenty-nine patients, 16 with RA and 13 with other inflammatory joint diseases, were investigated and compared to PBMC from 25 healthy controls. The mean number of IFN-gamma-producing cells was 37.1/10(5) plated SFMC (range 0-121.5). The corresponding value for PBMC was 5.1 (0-39). The difference was highly significant (P = 0.0033 for RA patients, P = 0.0050 for non-RA patients and P < 0.0001 for all patients). Forty-five per cent of SFMC samples (range for all samples 0-38.5 SFC/10(5) MNC) and 25% of PBMC samples (0-20.5) exhibited spontaneous IL-4 production, yielding a significant difference for all patients treated collectively (P = 0.021). Although the cells that spontaneously secrete these cytokines are relatively few, quantification of these cells thus shows increased functional T-cell activation and decreased ratio of cells spontaneously producing IL-4 vs IFN-gamma in the joint fluid as compared to blood of arthritis patients.