To evaluate the usefullness of SPECT thallium-201 exercise myocardial perfusion scan in coronary artery disease, polar maps processing SPECT images were compared to the exercise treadmill test and the findings of coronary angiographies in 12 normal subjects and 27 patients with the coronary artery disease. The following results were obtained : 1) Sensitivity and specificity of thallium-201 exercise myocardial perfusion scan was 96% and 83%, higher than that of exercise treadmill test(81% abd 61%). 2) In the branches of coronry artery, the sensitivity, specificity and positive predicitive values were 82%, 88%, 90% in left anterior descending artery, 33%, 88%, 57% in left circumflex artery and 69%, 81%, 90% 64% in right coronary artery. 3) The good correlation was observed between the degree of perfusion defect in polar map of thallium-201 myocardial scan in stress and 'myocardial ischemic score' predicted in coronary angiography(p<0.001). Also the degree of reversible perfusion defect had significant correlation with the durtion of exercise. 4) The pulmonary to myocardial ratio of thallium-201 uptake in coronary artery disease group higher than that of angina group. And the perfusion defect with stress and double product at maximal exercise had strongest assocition with the pulmonary to myocardial ratio of thallium-201 uptake by stepwise multiple linear regression. In conclusion, SPECT thallium-201 exercise myocardial perfusion scan is superior to the exercise treadmill test in diagnosing the coronary artery disese and is useful for predicting the sites and degree of coronary arterial stenosis. Also the pulmonary to myocardial ratio of thallium-201 uptake is thought to be good new test index in evaluating the left ventricular function of patients with coronary artery disease.