In order to evaluate the usefulness of a stress T1-201 myocardial scintigraphy in semiquantifying the myocardial perfusion, 10 normal subjects and 71 patients with coronary artery diseases were studied with sequential imaging over 3 hours. Myocardial to background ration (M/B) in the exercise phase was significantly higher in the normal subject group than in the coronary artery disease groups. Three hours after exercise (redistribution phase), M/B decreased significantly in the normal subject group but remained unchanged in the coronary artery disease groups. Percent change of M/B with exercise was lower in the effort angina pectoris group (97 +/- 11.2%), and the old myocardial infarction group (101 +/- 14.5%) than in the normal subject group (127 +/- 12%). Sensitivity and specificity of this method were 93% and 47%, respectively. Out of 11 patients with variant angina pectoris, 9 patients showed positive scintigram. Of the 9, however, 6 cases were without organic coronary stenosis in the coronary angiography. There was a significant correlation between M/B on redistribution images (RD.M/B) and ejection fraction determined by left ventriculograms (r = 0.61, p less than 0.001), indicating a close relation between the amount of the residual viable myocardium and the left ventricular function. M/B and its percent change with stress T1-201 myocardial scintigraphy reflect the myocardial perfusion and myocardial perfusion reserve and their semiquantitative analysis provides a useful means for detection of ischemic heart disease.