The anti-inflammatory activities of methotrexate and sulphasalazine may be mediated by increases in endogenous adenosine levels. Since the vascular protective drug dipyridamole inhibits the uptake and metabolism of adenosine we have now tested this compound in patients with rheumatoid arthritis to assess its effects on their symptoms. Forty patients (aged 18-75 years) received dipyridamole 400 mg/day or placebo. The levels of adenosine and its major metabolites were determined by high performance liquid chromatography (HPLC) in blood samples taken at baseline and at monthly intervals during treatment for 6 months. After three months of treatment there was a significant reduction in the modified Health Assessment Questionnaire (mHAQ) score, but these effects were not maintained, and dipyridamole did not modify disease severity scores or the levels of adenosine and its metabolites. We conclude that the symptoms of rheumatoid arthritis were not modified by treatment with dipyridamole.