ANCA are associated with small sized vessel vasculitis; one subtype is an antibody against myeloperoxidase(MPO), which stains in a perinuclear pattern(P-ANCA) indirect immunofluorescence(IIF) using a neutrophil substrate, and the other subtype is an antibody against proteinase-3(PR-3), which stains in a diffuse granular cytoplasmic pattern ANCA by IIF. PR-3 ANCA is more specific in Wegener's granulomatosis(WG) than the other primary vasculitides. MPO-ANCA can be found in microscopic polyangiitis (MPA), Churg Strauss Syndromes(CSS), drug-induced vasculitis, and environmental factor-induced such as silicosis vasculitis more frequently than WG. The value of the IIF test for ANCA detection can be greatly increased by the addition of a standardized antigen-specific ELISA. The intra-assay and inter-assay CV of the MPO and PR-3 ELISA were 6.6 to 4.8%, respectively. Close ANCA titer correlation was shown between MPO-ANCA ELISA and the activity of ANCA associated vasculitis. Renal manifestations and pulmonary manifestations are observed in 70-90% of AAV as the initial manifestation. The changes in titers of ANCA seem to reflect disease activity in 60-70% of AAV patients. A combination of steroids and immunosuppressive drugs is effective in relieving the clinical symptoms of AAV.