Patients with acute myocardial infarction undergoing primary angioplasty are at high risk for renal injury due to the toxic effect of contrast agents. Patients developing renal dysfunction after primary angioplasty have worse outcome. To investigate the role of the antioxidant N-acetylcysteine (NAC) in preventing renal injury in angioplasty, we randomized 352 consecutive patients undergoing primary angioplasty into three groups: the first group received NAC at standard dose (NAC group, 600 mg i.v. bolus before primary angioplasty, followed by oral 600 mg twice daily for the following 48 hours; n=115), the second group received NAC at double dose (DD-NAC group; 1,200 mg i.v. bolus and oral 1,200 mg twice daily for 48 hours; n=118), and the last group received placebo (controls; n=119).