Since adenosine receptor activation modulates the release of IL-10 by different inflammatory cells [25-27] and methotrexate-treated rheumatoid arthritis patients have shown increased serum levels of this cytokine [28,29], we determined whether constitutively or methotrexate-modified IL-10 accumulation in the inflammatory exudate was altered in adenosine receptor-deficient mice. The gene discussed is IL10; the disease is rheumatoid arthritis.