Non-invasive methods for evaluation of intravenous thrombolytic treatment in patients with acute myocardial infarction (AMI) are needed, since approximately 30% of the patients never obtain coronary reperfusion. These patients could be candidates for additional thrombolytic treatment or acute PTCA. This study included 63 AMI patients. Intravenous and/or intracoronary thrombolysis was given to 52 patients, and 11 patients received conservative treatment (placebo). Serum myoglobin was measured every 15 min. Acute coronary angiography showed a patent coronary artery in 49 patients ("Reperfusion" group), and 14 patients had no coronary reperfusion ("No-Reperfusion" group). Mean time to peak serum myoglobin was 149 (57-194) minutes in the "Reperfusion" group and 476 (330-660) minutes in the "No-Reperfusion" group, p < 0.0001. An observed peak serum myoglobin < 5 hrs. after initiation of intravenous thrombolysis would indicate coronary reperfusion with sensitivity = 0.94; specificity = 0.79; predictive values of positive and negative test: 0.94 and 0.79, respectively. It is concluded that an peak serum myoglobin < five hrs. after start of thrombolysis predicts reperfusion status with a high level of accuracy.