Elevated cytokine levels have been reported after ischemia/reperfusion injury and might cause a systemic inflammatory response syndrome (SIRS) after primary percutaneous coronary intervention (PPCI). High myeloperoxidase (MPO) levels are reported to be a risk factor for early cardiac events in patients with acute coronary syndrome. Its role as a predictor of SIRS in patients with ST-segment elevation myocardial infarction treated with PPCI is unclear. Therefore, the aim of the present study was to investigate the role of MPO as a predictor of SIRS in patients with ST-segment elevation myocardial infarction treated with PPCI. A total of 250 patients with ST-segment elevation myocardial infarction treated with PPCI were admitted to our coronary care unit. The serum MPO levels were measured at admission using a commercially available enzyme-linked immunosorbent assay. Of the 250 patients, 47 developed SIRS within 48 hours after their admission to the coronary care unit; 10 of these patients were excluded from analysis because of the suspicion of sepsis. The remaining 203 patients had no SIRS during their coronary care unit stay. Compared to patients without SIRS, those with SIRS had greater serum MPO values (81.35 +/- 18.07 vs 67.03 +/- 16.98 ng/ml, p <0.0001) after PPCI. After controlling for different baseline clinical, laboratory, and angiographic variables, the baseline serum MPO levels were an independent predictor of SIRS (odds ratio 4.2, 95% confidence interval 1.9 to 8.4, p <0.001). In conclusion, our results have demonstrated that MPO is an independent predictor of SIRS after PPCI, suggesting a new clue for the interpretation of this phenomenon.