A minimum of 22 visits to the clinic will be required to complete the entire study. Patients will undergo a comprehensive medical evaluation, with laboratory studies and x-rays. There may also be consultations and possible biopsies of affected organs only if medically indicated for diagnosis and treatment of the disease. In the 4-week period that patients will receive rituximab infusions, the methotrexate or azathioprine will be continued at the same dosage unless there are side effects that requite the medication to be temporarily stopped or the dosage reduced. Patients will receive four doses of rituximab, at 375 mg per meter squared of body surface area, once a week. It will be infused into a vein, through an intravenous catheter. For the first dose, patients will be admitted as inpatients for at least 24 hours, for monitoring during the infusion and for any reactions associated with it. The second, third, and fourth rituximab infusions may be given either on an inpatient or outpatient basis to be decided on how the patient tolerates the first infusion.