Platelet aggregation inhibition (PAI) of ≥95% has been associated with improved outcomes after percutaneous coronary intervention (PCI) and glycoprotein IIb/IIIa inhibitor treatment. A greater thrombotic burden in acute ST-segment elevation myocardial infarction (STEMI) might require higher doses and/or intracoronary delivery of glycoprotein IIb/IIIa inhibitors to achieve optimal PAI. Using a 2 × 2 factorial placebo-controlled design, 105 patients with STEMI who had been referred for primary PCI within 6 hours of symptom onset were randomized to intracoronary (IC) or intravenous (IV) delivery of an abciximab bolus at a standard dose (0.25 mg/kg) or high dose (≥0.30 mg/kg) of abciximab. The primary end point was PAI measured at 10 minutes after the bolus of abciximab. Secondary end points included the acute and 6-month outcomes using angiographic parameters, cardiac biomarkers, cardiovascular magnetic resonance imaging, and clinical end points. At 10 minutes after the bolus, the proportion of patients with ≥95% PAI was not different between the IC and IV groups (53% vs 54%, p = 1.00) nor between the high-dose and standard-dose bolus groups (56% vs 51%, p = 0.70). Acutely, the angiographic myocardial blush grades, peak release of cardiac biomarkers, necrosis size, myocardial perfusion, and no reflow as assessed by magnetic resonance imaging, and clinical end points were similar between the groups and did not suggest a benefit for IC compared to IV or high-dose versus standard-dose bolus of abciximab. No increase occurred in bleeding complications with the high-dose bolus or IC delivery. The clinical, angiographic and cardiac magnetic resonance imaging outcomes at 6 and 12 months were similar between the 4 groups. In conclusion, in patients with STEMI presenting with symptom onset <6 hours and undergoing transradial primary PCI, PAI remained suboptimal, despite a higher dose bolus of abciximab. A higher dose bolus or IC delivery of abciximab bolus was not associated with improved acute or late results compared to the standard IV dosing and administration.