Juvenile rheumatoid arthritis: Under 16 years of age at onset Arthritis in 1 or more joints as defined by swelling or effusion, or presence of 2 or more of the following: Limitation of range of motion Tenderness or pain on motion Increased heat Duration of disease 6 weeks or longer Onset type defined by type of disease in first 6 months: Polyarthritis (i.e., 5 or more inflamed joints) Oligoarthritis (i.e., less than 5 inflamed joints) Systemic (i.e., arthritis with characteristic fever) Exclusion of other forms of juvenile arthritis Active disease evidenced by 1 of the following: Minimum of 2 swollen or tender joints using the 71 joint count method Endocardial or myocardial disease, or serositis Anemia or thrombocytosis of chronic disease High risk for developing deforming joint disease or evidence of potential life threatening involvement for at least 1 internal organ system Radiographic evidence of erosive arthritis developing within first 24 months of clinical disease Functional class II or III Endocardial, myocardial, pericardial, and/or pleural disease Hemoglobin less than 10.0 g/dL or platelet count greater than 600,000/mm3 Refractory to conventional therapy after 12 months of methotrexate used in combination with hydroxychloroquine, sulfasalazine, azathioprine, cyclosporine, or cyclophosphamide OR Controlled on conventional therapy but at price of unacceptable toxicity