Purpose: Cost-effectiveness of myocardial SPECT f'or the diagniosis of coronary artery disease was investigated considering the present and amended costs of myocardial SPECT and exercise ECG in Korea. Materials and Methods: Four diagnostic tactics such as 1) coronary angiography (CAG) after exercise ECG, 2) CAG after myocardial SPECT, 3) direct CAG, and 4) CAG after myocardial SPECT following exercise ECG were chosen. Costs were calculated using the present costs of various tests and effects represented by Quality Adjusted Life Year (QALY) were estimated. Difference of QALY (ΔQALY) was calculated by subtracting QALY of diagnosed/treated cases from QALY of undiagnosed cases, Cost/Δ QALY was calculated and compared between four different tactics according to pre-test probability, Results: When pre-test probability was equal to or larger than 0.6, direct CAG was the most cost-effective. When pre-test probability was between 0.2 and 0.6, CAG after myocardial SPECT following exercise ECG was the most cost-effective. CAG after myocardial SPECT was the second most cost-effective. Cost-effectiveness was similar when the costs of exercise ECG were doubled or quadrupled. CAG after exercise ECG was always the least cost-effective, Conclusion: Myocardial SPECT with or without preceding exercise ECG was the most cost-effective method to diagnose coronary artery disease in the present or expected amended cost system. (Korean J Nucl Med 2000;34:207-21)