To estimate the size of myocardial infarction, serum troponin T concentration was measured in 34 patients with acute myocardial infarction. Left ventriculography, 2-dimensional echocardiography and resting ^20lthallium myocardial single photon emission computed tomography (SPECT) were performed about 4 weeks after the onset of myocardial infarction and used for correlation with the late serum troponin T peak concentration which occurred on the 3rd to 5th day after onset. Both left ventricular ejection fraction (LVEF) obtained from left ventriculography and wall motion index (WMI) obtained from 2-dimension-al echocardiography were inversely related to late troponin T peak value (LVEF: r=-0.68, p<0.001, WMI: r=-0.70, p<0.001). Extent score (ES) and severity score (SS), which were estimated from the initial resting ^20lthallium SPECT image, showed excellent linear correlations with late troponin T peak concentrations (ES: r=0.77, p<0.001, SS: r=0.66, p<0.001). This correlation was present both in patients with an early troponin T peak on day 1 (group A-16 patients) and in those without an early peak (group B-10 patients). Thus, late troponin T peak concentration can be used to predict infarct size regardless of the kinetics of its appearance in serum.