Interleukin-1 beta, interleukin-2, tumour necrosis factor alpha, and the interferons, alfa and gamma, were measured concurrently in synovial fluid samples from 68 patients with rheumatic diseases. Mean interleukin-1 beta concentrations (130.3 (SD 22) pg/ml) were higher in synovial fluids from patients with rheumatoid arthritis (RA) than in those from patients with osteoarthritis (27.8(4.5)pg/ml), while measurements in synovial fluids from patients with seronegative spondarthritis were intermediate (72.7 (32) pg/ml). Interleukin-2 and tumour necrosis factor alpha concentrations were lower in the inflammatory arthropathies (RA: 4.5 (0.6) U/ml, 0.39 (0.04) ng/ml; seronegative spondarthritis: 3.1 (0.3) U/ml, 0.33 (0.03) ng/ml respectively) than those in patients with osteoarthritis (5.2 (0.6) U/ml; 0.05 (0.04) ng/ml). Interleukin-2 and tumour necrosis factor alpha concentrations correlated in all groups (r = 0.7), as did the interferons alfa and gamma (r = 0.7). There was no relation between interleukin-1 beta and either interleukin-2 or tumour necrosis factor alpha, or between the interferons and any other cytokine. Several distinct cytokine patterns were noted. Synovial fluids from two non-arthritic subjects were also examined: interleukin-1 beta concentrations were low, but concentrations of the other cytokines were higher than those seen in most arthritic fluids.