We investigated serum levels of interleukin (IL)-1 beta, IL-6, IL-8, IL-12 and tumour necrosis factor (TNF)-alpha in JRA patients during both active and inactive phases of the disease. The systemic JRA patients had the highest IL-1 beta and IL-6 levels during both active and inactive periods. In the systemic group IL-1 beta, IL-6 and IL-12 levels during the active period were elevated compared to the inactive period (p = 0.0173, p = 0.0359 and p = 0.0117, respectively). Levels of these cytokines during the inactive stage were still greater than those of controls. IL-8 and TNF-alpha. levels during both active and inactive periods were comparable to controls. IL-1 beta correlated strongly with CRP and ESR (p = 0.008 and p = 0.031, respectively). IL-6 correlated significantly with CRP (p = 0.002). IL-12 levels were found to be correlated with ESR and CRP (p = 0.03 and p = 0.04, respectively). In active polyarticular JRA patients, IL-6 levels were elevated compared to the inactive phase, and the control (p = 0.001) IL-12 levels decreased significantly with clinical remission (p = 0.018). There was a strong correlation between Il-12 levels and number of joint with limited motion (p = 0). In oligoarticular JRA patients, IL-12 levels during active period were greater than in the controls and there was a marked decrease in IL-12 levels when the patients entered the inactive phase (p = 0.001) In conclusion, IL-1 beta, IL-6 and IL-12 may play an important role in JRA and may be used as a marker of disease activity.