Intravenous thrombolytic therapy has become a routine therapeutic intervention in acute myocardial infarction. In order to evaluate its success in the general hospital community noninvasive methods are needed. Therefore, the effect of infarct reperfusion on the times to peak value of myoglobin, CKMB, and CK were studied in patients with acute myocardial infarction. Recanalization of the occluded coronary artery was achieved by intracoronary infusion of streptokinase in eight patients within 3.5 h, and in 18 patients more than 3.5h after onset of pain. In 10 patients, the coronary artery remained occluded, and in eight patients thrombolysis was not attempted. Analyzing the times to peak value of myoglobin, CKMB, and CK, the probability of correct classification of infarct reperfusion varied between 1 and 0.9, if recanalization was achieved within 3.5 h after onset of pain. The predictive power could be improved further by a combined analysis of the times to peak value of both myoglobin and CK. In cases where reperfusion was achieved more than 3.5 h after the onset of pain, the probability of correct classification of infarct reperfusion varied between 0.99 and 0.05. Among the marker proteins analyzed, myoglobin allowed the earliest and best discrimination between reperfusion or no reperfusion. Thus, by applying the time to peak value analysis, infarct reperfusion can only be predicted reliably if it is achieved early after onset of pain.