Cytokines are major mediators of inflammatory responses in rheumatoid arthritis. Some of them have been shown to correlate with the disease activity and thus are proposed to be used for monitoring patients. Therefore the effects of a low-dose therapy with methotrexate on serum concentrations of interleukin-6 (IL-6) and tumour-necrosis-factor-alpha (TNF-alpha) were examined in eight patients with seropositive rheumatoid arthritis. Serum levels of IL-6 and TNF-alpha were significantly elevated in patients compared to healthy controls. Before the onset of MTX treatment IL-6 concentrations were correlated to the c-reactive protein (P < 0.05) but the correlation was abolished after treatment. For TNF-alpha no correlations neither before nor after treatment were observed. Both cytokines remained substantially elevated after MTX treatment despite a clear reduction in disease activity. Thus we suggest that one of the effects of MTX might be the inhibition of some of the actions of IL-6 and TNF-alpha.