Wegener's granulomatosis and the Churg-Strauss syndrome are both syndromes that appear to begin with a phase of regionally limited symptomatology before they progress at unpredictable rate to a generalized phase characterized by symptoms of systemic vasculitis. The clinical features of atopy, peripheral blood eosinophilia, and tissue eosinophilia distinguish CSS from WG, with its typical necrotizing granulomatous respiratory tract lesions. Whereas in generalized WG with renal involvement the use of cyclophosphamide usually cannot be avoided, the generalized systemic vasculitis phase of CSS appears to respond well to glucocorticoids alone. For the more limited forms of WG, adapted therapy regimens including trimethoprim-sulfamethoxazole have been reported to be successful. Anticytoplasmic autoantibodies (c-ANCA = ACPA) are a new diagnostic serum test with high specificity for WG. Serial determinations of c-ANCA are a promising tool to monitor disease activity.