Adenosine can suppress the release of tumour necrosis factor-alpha (TNF-alpha) from activated monocytes and macrophages, and may contribute to the anti-inflammatory activities of methotrexate and sulphasalazine. Dipyridamole inhibits the cellular uptake and metabolism of adenosine and we have, therefore, examined the effects of dipyridamole in patients with rheumatoid arthritis in an attempt to alleviate their symptoms. Forty patients aged 18-75 years were randomised to receive dipyridamole 400 mg/day or placebo. Blood samples were taken at baseline and at monthly intervals for 6 months. Purines were determined by HPLC and cytokines by ELISA. After 3 months of treatment there were significant reductions in neopterin levels and in the modified Health Assessment Questionnaire score, but these were not maintained. Dipyridamole had no effect on disease severity or the levels of purine metabolites, interleukin-1beta (IL-1beta), IL-6, TNF-alpha, lipid peroxidation products, erythrocyte sedimentation rate or C-reactive protein. In conclusion, rheumatoid arthritis patients showed no clinical improvement following treatment with dipyridamole for 6 months.