Twenty-one patients with myeloperoxidase-antineutrophil cytoplasmic autoantibody (MPO-ANCA)-associated vasculitis were treated using cytapheresis. Of these, 17 were treated for glomerulonephritis and four were treated for pulmonary hemorrhage. The overall survival rate was 85.7% with a follow-up duration of 24.0 +/- 13.8 months. In the 17 patients with MPO-ANCA-associated glomerulonephritis, pretreatment creatinine was 3.2 +/- 1.6 mg/dL, and renal function recovered in 76.5%. Pulmonary hemorrhage was ameliorated in all four patients. Abdominal pain occurred in three of the 21 patients but symptoms resolved soon after the cytapheresis procedure was completed. No other adverse effects occurred during cytapheresis. From these results, cytapheresis can be considered a safe and effective treatment for MPO-ANCA-associated vasculitis. As for the mechanism of its action, soluble tumor necrosis factor receptor 1 (sTNFR), sTNFR2 and interleukin 1 receptor antagonist were elevated soon after cytapheresis and those levels 2 h after the cytapheresis procedure were higher than before the procedure in some cases. These elevations might be related to the efficacy of cytapheresis.