Objective.To compare the clinical and pathological manifestations of patients with antineutrophil cytoplasmic autoantibodies (ANCA) directed against proteinase 3 (anti PR3) or myeloperoxidase (anti MPO). Methods.One hundred and forty patients with ANCA were detected for anti PR3 and anti MPO by ELISA.The clinical features at presentation,histopathological characteristics and outcome of all patients who were tested positive for anti PR3 or anti MPO were analysed. Results.In anti PR3 group (n=21),16 cases (76.2% ) had systemic vasculitis,in which Wegeners granulomatosis prevailed (13 cases,61.9% ).In anti MPO group (n=31),19 cases (61.3% ) were diagnosed as systemic vasculitis and 12 cases (38.7% ) as microscopic angiitis.For vasculitic patients with anti PR3 and anti MPO,the disease duration at diagnosis was 9.6± 2.0m and 4.4± 0.9m respectively,P0.05;upper respiratory tract,eye and joint involvements were 11(68.8% ),7(43.8% ),11(68.8% ) and 7(36.8% ),2(10.5% ),5(26.3% ) respectively,P500 μ mol/L were more commonly seen in anti MPO group than in anti PR3 group,which were 8(42.1% ) and 2(12.5% ) respectively,P< 0.05.Ten relapses were seen in anti PR3 group and only 2 in anti MPO group,but the acute mortality rate in anti MPO group (5/19,27.4% ) was much higher than that in anti PR3 group (1/16,6.3% ). Conclusions.Anti PR3 and anti MPO occurred mainly in systemic vasculitis.A large divergence was seen in the disease spectrum between patients with anti PR3 and those with anti MPO.In particular,upper respiratory tract,eye and joint involvements,granuloma formation and relapse were more prominent in anti PR3 patients.By contrast,the anti MPO patients had a more acute disease onset,more rapid progressive renal involvement and a higher acute mortality rate.