NTINEUTROPHIL CYTOPLASmic antibodies (ANCAs) are frequently found in patients with Wegener granulomatosis and microscopic polyangiitis. Together, Wegener granulomatosis and microscopic polyangiitis are considered ANCA-associated vasculitis (AAV) due to their similarity in clinical and histological features, prognosis, and treatment. Standard therapy for patients with AAV consists of induction of remission with cyclophosphamide and glucocorticoids, followed by remission maintenance with azathioprine or methotrexate and a tapering course of glucocorticoids. 1,2 Relapses of AAV occur in 50% of patients within 5 years of diagnosis, and treatment toxicity is common. 3,4 Safe and effective therapies to maintain remission of AAV are a priority. For editorial comment see p 2413.