Anti-myeloperoxidase (MPO) antibodies are associated with the development of anti-neutrophil cytoplasmic antibody (ANCA)-related vasculitis. The imbalance between the protease- anti protease activity in the neutrophils has been implicated in the pathogenesis of ANCA-related vasculitis. Ceruloplasmin is an acute-phase protein that has antiproteinase and antioxidant properties and inhibits MPO activity. We attempted to study the association between serum ceruloplasmin and ANCA in childhood vasculitis. Forty-five ANCA-related diseases were included in the study. The age range was 4-16 years. Patients were divided into two groups based on indirect immunofluorescence and/or ELISA specificity (MPO). Twenty-six patients had p-ANCA- and 19 patients had c-ANCA-positive disease. Nine patients with Henoch-Schonlein purpura were studied as an ANCA-negative control group. Serum ceruloplasmin levels in p-ANCA-, c-ANCA-positive patients, and controls were 125.85 +/- 93.48 mg/dl, 59.79 +/- 17.60 mg/dl, and 64.34 +/- 18.77 mg/dl, respectively, and were significantly higher in patients with p-ANCA (P<0.05). Ceruloplasmin levels were significantly decreased in remission (P<0.05). Median MPO level in p-ANCA-positive patients was 15.2 (5-250) and was negative in all c-ANCA-positive patients. There was a significant positive correlation between MPO and ceruloplasmin levels: (r=0.70, P<0.05). Of 26 patients (53.8%) in the p-ANCA-positive group, 14 had renal involvement. The patients with renal disease had significantly higher ceruloplasmin levels than others (151.17 &PLUSMN; 92.14 and 134.64 &PLUSMN; 95.16 mg/dl respectively, P<0.05). In conclusion, the increase in ceruloplasmin levels during the acute phase suggests that this might be an activation criterion or a response to neutrophil-mediated tissue injury. Increased ceruloplasmin levels together with p-ANCA positivity may be predictive for renal involvement and a serious clinical course. The correlation between ceruloplasmin and MPO levels supports their association. Further studies are necessary to elucidate whether genetic and/or functional alterations in ceruloplasmin are effective in the pathogenesis of vasculitis.