All participants will receive 20 Mg./week of methotrexate. In addition, patients will be randomly assigned to receive a monthly infusion of infliximab or placebo (a fluid that contains no active drug). After 6 months, all patients will receive active infliximab for the remaining half year of the study. Patients will also receive folic acid (1mg/day), Vitamin D (400 IU/day), and calcium supplements. They may continue to take prednisone (no more than 10 Mg./day) and non-steroidal anti-inflammatory drugs (NSAIDS). Medication dosages will be adjusted as needed if pain and joint swelling worsen. Over the course of the study, patients will come to NIH for 15 visits and undergo the following tests and procedures: