The aim of this study was to investigate the role of neutrophil activation, protein oxidation and ceruloplasmin (CLP) in the pathogenesis of Henoch-Schönlein purpura (HSP), which has not been investigated previously. Serum activities of myeloperoxidase (MPO) and arylesterase (ARYL) and levels of free thiol groups, CLP and total oxidant status (TOS) were measured in 29 children with HSP at the onset of the disease and during remission in comparison with 30 healthy subjects. Patients at active stage had significantly higher MPO activity (391+/-277 vs. 155+/-154 U/l, P<0.001), higher CLP (832+/-120 vs. 682+/-114 mg/dl, P<0.001) and TOS values (20.7+/-11.8 vs. 7.5+/-2.8 micromol H2O2/l, P<0.001) than the controls, respectively. Patients had significantly lower ARYL activity (158x10(3)+/-39x10(3) vs. 187x10(3)+/-46x10(3) U/l, P<0.001) and lower free thiol levels (234+/-48 vs. 279+/-26 micromol/l, P<0.001) than the controls, respectively. Significantly positive correlations were found between TOS and MPO (r=0.437, P=0.018) and TOS and CLP (r=0.409, P=0.028) at disease onset, whereas a negative correlation was found between MPO and thiol (r=-0.597, P=0.001) during remission. In conclusion, protein oxidation and neutrophil activation may play important roles in the pathogenesis of HSP. Further research is required to understand the potential linkage between oxidant stress and complications and to develop therapeutic strategies in HSP.