OBJECTIVE To evaluate the importance of the segment ST in the identification of coronary recanalization in patients submitted to intravenous thrombolysis during acute myocardial infarction (MI). METHODS Seventy four patients with MI, 62 male with mean age of 52.6 +/- 10 years. All patients had angiographically demonstrated occlusion of the infarct-related artery (IRA) before the thrombolytic treatment with intravenous "in bolus" infusion of 50 mg, 60 mg and 70 mg of rt-PA. The recanalization of the IRA was assessed 90 minutes later. The real status of the IRA in the angiograms was compared with the ST segment changes between the ECGs obtained before and after the thrombolytic therapy. RESULTS Fifty six (75.6%) patients presented a significant reduction in the ST segment elevation (groups I and II). Of these, 47 possessed an opened IRA. From the 18 patients who did not show ST segment decrement (group III), 13 had an occluded IRA, and 5 an opened one. The method presented sensitivity of 90.3% and a specificity of 59.1%, positive predictive value of 83.9% and negative predictive value of 72.2%. CONCLUSIONS The ST segment is an important marker of coronary recanalization or not following intravenous thrombolytic therapy.