The purpose of this study is to assess the comparative efficacy of using methotrexate versus mycophenolate mofetil for maintaining remission that has been induced by cyclophosphamide and glucocorticoids in patients with Wegener's granulomatosis and related vasculitides. In this study, all patients will initially receive daily cyclophosphamide and glucocorticoids and then at disease remission, cyclophosphamide will be discontinued and patients will be randomized to receive either methotrexate or mycophenolate mofetil for remission maintenance. They will continue to receive the agent to which they are randomized for 2 years, after which time it will be tapered and discontinued. Patients will be prospectively monitored for evidence of disease relapse and drug toxicity. Specific parameters that will be obtained include the time to disease remission, the rate and time of disease relapse, and the incidence of drug-related adverse events.