Inflammation plays a critical role in acute myocardial infarction. One inflammatory marker is myeloperoxidase (MPO). Its role as a predictor of in-hospital death in patients with ST-segment elevation myocardial infarction (STEMI) presenting with cardiogenic shock (CS) is unclear. Therefore, the aim of this study was to investigate the role of MPO as a predictor of in-hospital death in patients with STEMIs presenting with CS and treated with primary percutaneous coronary intervention. In 38 consecutive patients with CS complicating STEMIs who were treated with primary percutaneous coronary intervention, serum MPO levels were measured at coronary care unit admission using a commercially available enzyme-linked immunosorbent assay. The primary study end point was in-hospital cardiac death. Among the 38 patients included in the study, 20 died during their coronary care unit stays, whereas 18 survived. Compared with patients who survived, patients who died showed, at coronary care unit admission, higher serum MPO levels (81 +/- 28 vs 56 +/- 23 ng/ml, p <0.006). After controlling for different baseline clinical, laboratory, and angiographic variables, baseline serum MPO level was an independent predictor of in-hospital mortality on multivariate analysis (odds ratio 3.9, 95% confidence interval 1.8 to 7.5, p <0.001). In conclusion, admission MPO concentration is an independent predictor of in-hospital mortality in patients with STEMIs presenting with CS.