Juvenile Rheumatoid Arthritis (JRA) is an autoimmune disease characterized by chronic joint inflammation. Oxygen free radicals are an important initiator of tissue damage in JRA. A deficiency of antioxidants that would lead to increased exposure to oxygen free radicals could therefore play a major role in disease manifestation. Nitric oxide is a free radical involved in inflammation and immune reactions and its generation may be important in the pathogenesis of JRA. The serum concentration of NO proved to be significantly higher in JRA and associated with disease activity.