Two children of 9 and 10 years suffering from severe systemic juvenile rheumatoid arthritis were treated intravenously with high-dose human immunoglobulin. Treatment was performed every 4 weeks for 7 and 18 months, respectively. Improvement of arthritic symptoms was demonstrable by significant decreases of Ritchie index and number of swollen joints and the disappearance of heated joints in one patient. The other patient was free of arthritic symptoms since the introduction of immunoglobulin therapy. Clinical symptoms of systemic illness were markedly improved and no relapse was seen. Laboratory parameters also improved, including erythrocyte sedimentation rate, C-reactive protein, hemoglobin, and serum iron levels. Parallel investigations of immunological parameters revealed a decrease of serum Il-1 beta and Il-6 levels and a diminished in vitro production of Il-1 beta, Il-6, and tumor necrosis factor-alpha. Therefore, we suggest a decreased activation status of the monocyte-macrophage system as one possible mode of action.