To compare the clinical and pathological manifestations of patients with antineutrophil cytoplasmic autoantibodies （ANCA） directed against proteinas e 3 （anti PR3） or myeloperoxidase （anti MPO）. Methods. One hundred and forty patients with ANCA were detected for anti PR3 a nd anti MPO by ELISA. The clinical features at presentation

histopathological characteristics and outcome of all patients who were tested positive for anti P R3 or anti MPO were analysed.Results. In anti PR3 group （n=21）

16 cases （76.2%） had systemic vasculitis

in which Wegener’s granulomatosis prevailed （13 cases

61.9%）. In anti MPO g roup （n=31）

19 cases （61.3%） were diagnosed as systemic vasculitis and 12 case s （38.7%） as microscopic angiitis. For vasculitic patients with anti PR3 and a nti MPO

the disease duration at diagnosis was 9.6±2.0m and 4.4±0.9m respecti vely

P< 0.05;vasculitis activity index （BVAS） and mean number of affected organ were 22.5±2.1

5.0±0.4 and 25.1±1.7

4.8±0.4 respectively

P >0.05;upper r espiratory 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

P< 0.05.Although there was no statistical difference in renal involvement between these two groups

patien ts with serum creatine >500 μmol/L were more commonly seen in anti MPO group t han 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 t he acute mortality rate in anti MPO group （5/19

27.4%） was much higher than t hat 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 PR 3 and those with anti MPO. In particular

upper respiratory tract

eye and join t involvements

granuloma formation and relapse were more prominent in anti PR3 patients. By contrast

the anti MPO patients had a more acute disease onset

m ore rapid progressive renal involvement and a higher acute mortality rate.