We report here 4 patients with Churg-Strauss syndrome (CSS) who had classic symptoms including a history of bronchial asthma, severe eosinophilia and necrotizing vasculitis. The antineutrophil antibody (ANCA) against myeloperoxidase (MPO) titers was elevated (44-877 ELISA units), but the ANCA against proteinase-3 (PR3) was negative in all patients. One case was complicated with systemic inflammatory response syndrome (SIRS) and required plasmapheresis and continuous hemodiafiltration. One other patient clinically showed rapidly progressive glomerulonephritis and had hemodialysis 24 times. Two of 4 patients showed good responses with corticosteroid therapy alone, while 2 patients required the addition of cyclophosphamide. Urinary abnormalities such as proteinuria or microscopic hematuria were found in all patients. Three patients had a decreased glomerular filtration rate (GFR) and renal biopsy specimens obtained from these patients showed crescentic glomerulonephritis. One patient had mild to moderate mesangial-proliferative glomerulonephritis with interstitial eosinophilic infiltration. These findings suggest that renal involvements in CSS may not be as uncommon a disorder as previously considered, especially when MPO-ANCA is positive. MPO-ANCA may be associated with the onset of glomerular disorders in CSS.