Patients 10 to 80 years of age with active Wegener's granulomatosis, polyarteritis nodosa or a related systemic vasculitis may be eligible for this study. Candidates will be screened with a medical history and physical examination, blood and urine tests, chest X-ray, electrocardiogram (EKG) and pulmonary function tests. Other procedures, such as biopsies, will be done only as medically indicated.