We will exclude from the study people who have recently taken systemic corticosteroids, people taking oral contraceptives, smokers, and pregnant women because these factors have been shown to significantly lower bone mineralization. We will withdraw subjects from the study if they demonstrate an elevated fasting random urinary calcium/creatinine ratio (>0.2), a chronic disease in addition to JRA that affects growth or bone mineralization, or they become pregnant. We will include these patients and all those withdrawing from the study voluntarily in an "intention-to-treat" analysis.