Patients with Wegener's granulomatosis or other related blood vessel disorders between 10 and 80 years old will be considered for this study. All participants will start therapy with daily doses of prednisone and cyclophosphamide. Prednisone will be reduced gradually and then stopped after symptoms improve significantly. Cyclophosphamide will continue until the disease is in remission. Patients in remission will then be randomly assigned to continue treatment with either MPM or methotrexate. MPM is taken twice a day by mouth. Methotrexate is taken once a week, usually by mouth, but in some cases, by injection into a muscle or under the skin. Patients who do well and have no side effects will continue treatment for 2 years. Then, the drug will gradually be reduced (usually at monthly intervals) and finally stopped. No further treatment will be given unless a relapse occurs. At that time, the type of treatment will depend on various medical factors, including the severity of the recurrence and the patient's history of drug side effects.