Background: The aim of this study is to carify the effect of intracoronary (IC) administration of a bolus dose of abciximab during percutaneous coronary intervention (PCI) in the patient with ST segment elevation myocardial infarction(STEMI) due to thrombotic total obstruction of culprit artery. Methods: We studied 73 patients with STEMI who underwent primary PCI after administration of an IC abciximab bolus (0.25 mg/kg) (IC Group, 36 pateints, 56.9짹13.9 years), and control patients who were treated by intravenous (IV) bolus and conventional maintainace dose(10 microgram/kg for 12 hours) of abciximab (IV Group, 37 patients, 57.9짹10.8 years) prior to balloon inflation. Myocardial blush grade(MBG) after PCI, incidence of bleeding complication, and in-hospital, 6, 12 months major adverse cardiac event (MACE; death, myocardial infarction, urgent revascularization) were assessed. Results: There were no significant differences between two groups with regard to baseline clinical, and angiographic characteristics. The dosage of abciximab was significantly higher in IV group than IC group(29.6짹1.7 mg vs. 13.9짹4.8 mg, P<0.001). The success rate of intervention also showed no significant differences between the two groups. After administration of abciximab, MBG after primary PCI were significantly higher in IC group than IV group(2.5짹1.7 vs. 1.2짹1.4, P=0.01). The incidence of bleeding complication showed no significant differences, but a trend toward reduction in IC Group (4.8%) compared with IV Group (6.8%) was observed. The length of in-hospital stay was significantly longer in IV group than IC group(7.7짹4.4 days vs. 4.9짹1.5 days, P=0.001). The incidence of in-hospital death was significantly higher in IV group than IC group(4 vs.0, P=0.044). The 6 and 12 months MACE were not significantly different. Conclusion: The IC administration of bolus dose of abciximab acutely increased MBG, decreased bleeding complication and hospital stay, and inhospital death in patients with STEMI undergoing primary PCI. Further large scale studies are warranted to evaluate the potential clinical benefits associated with IC abciximab administration.