Plasma advanced oxidation protein products (AOPP) are a biomarker for increased production of reactive oxygen species. We examined the possible association between pain to hospital time, plasma AOPP, and outcome of patients receiving percutaneous coronary intervention (PCI) for ST-elevation acute myocardial infarction (STEMI). Plasma AOPP was determined at hospitalization as well as 24 and 48 h after PCI in 79 patients with suspected STEMI. Patients were stratified into a control group (Group I, n = 21) after exclusion of coronary artery disease, Group II (n = 46) with pain to hospital time <12 h, and Group III (n = 33) with pain to hospital time >12 h. Associations between pain to hospital time and AOPP as well as incidence of major adverse cardiac events (MACE) during 6 months of follow-up were analyzed. Plasma AOPP at admission was significantly higher in patients of Group II (97.58 +/- 23.41 micromol/l) and Group III (184.52 +/- 30.41 micromol/l) in comparison with Group I (57.41 +/- 13.60 micromol/l, all P < 0.001). Plasma AOPP concentration was positively correlated with pain to hospital time and associated with an increased incidence of MACE during the 6-month follow-up period. Prolonged ischemia is associated with increased oxidative stress and poor prognosis in patients treated with PCI for STEMI.