Interleukin 1-beta (IL-1 beta), IL-2, IL-4, IL-5, IL-6, IL-8, tumour necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta) and granulocyte-macrophage colony-stimulating factor (GM-CSF) gene expression was determined in knee synovium of 16 patients with rheumatoid arthritis (RA) and 16 patients with seronegative spondyloarthropathies (SSP), by using polymerase chain reaction (PCR) amplification. The pattern of cytokines observed in RA synovium is of the macrophage-fibroblast type, with the highest expression of IL-1 beta and TGF-beta. GM-CSF and IL-2 bands were visualized in a minority of patients. Neither IL-4 nor IL-5 could be detected. No significant differences were observed in the cytokine profile between patients with early (< 12 months) and more advanced disease. No differences were observed according to gender, age, rheumatoid factor status and the duration of knee synovitis. The pattern of cytokines in the synovium of SSP patients is similar to that observed in RA patients and does not change in relation to disease duration. IL-2 was the only T-cell cytokine observed. These data provide evidence that the macrophage-fibroblast cells have an important role in early and more advanced rheumatoid synovitis, and show that this is also true for SSP peripheral synovitis.