In the last few years the important role played by various cytokines in the pathogenesis of chronic inflammatory diseases has emerged. In the present study, serum and synovial fluid levels of IL-2, IL-6, TNF alpha, IFN beta and IFN gamma were evaluated in a group of 66 patients with juvenile chronic arthritis (JCA). At the same time the ESR, CRP, hemoglobin, immunoglobulins, platelet count and Ritchie index were measured. In the serum of pauciarticular patients, IL-6 and TNF alpha levels were only slightly elevated compared with controls, but there was no correlation between these cytokines and clinical and other laboratory parameters. Serum IL-2 and IFN gamma were undetectable. In contrast, in the synovial fluid IL-6 levels were very high in all of the patients examined and there was a significant correlation between synovial fluid IL-6 levels and Ritchie's articular index. TNF alpha tended to be elevated but to a lesser extent, while synovial fluid IL-2 and IFN gamma were undetectable or very low, as in the serum. In polyarticular and systemic patients, on the other hand, serum IL-6 was elevated and statistically correlated with the majority of the laboratory parameters and with the Ritchie articular index. TNF alpha levels were only slightly elevated; on the other hand, IL-2 and IFN gamma were undetectable. There was an inverse correlation between IFN beta levels and the Ritchie articular index and a significant correlation with hemoglobin levels. In conclusion, our study demonstrates that not only IL-1 (as shown in other studies), but also IL-6 and to a lesser extent TNF alpha play a central role in the pathogenesis of JCA. IFN beta on the other hand, would seem to play an anti-inflammatory role.