To determine the indication for coronary revascularization (A-C bypass and PTCA), we performed thallium(Tl)-201 scintigraphy and contrast left ventriculography (LVG) in 25 cases who had A-C bypass surgery and 22 cases who had PTCA. The Tl uptake in the delayed image (Tl score = normal: 3, mild hypoperfusion: 2, severe hypoperfusion: 1, defect: 0), the presence of redistribution, and regional wall motion by LVG (LVG score = normal: 3, reduced: 2, none: 1, dyskinesis: 0), were compared with each other before and after revascularization. Sensitivity, specificity and accuracy of myocardial viability as evaluated by each index were; the presence of redistribution; 96%, 35%, and 60%; Tl score much greater than 2; 83%, 33%, and 66%; Tl score much greater than 1; 81%, 75%, and 81%; LVG score much greater than 2; 80%, 29%, and 63%; and LVG score much greater than 1; 79%, 33%, and 74%; respectively. It was difficult to evaluate the myocardial viability only by the presence of redistribution. However, any case with redistribution was a prime candidate for coronary revascularization. The Tl score much greater than 1 was the most reliable indication using the individual index. Although the diagnostic accuracies of the Tl and LVG scores were superior to the presence of redistribution, there was no individual index of myocardial viability common to all cases. If there were clinical necessity and angiographic indication, coronary revascularization could be tried in all cases except those whose Tl and LVG scores were both 0. In conclusion, myocardial viability can be evaluated scintigraphically only by the delayed image and by the presence of redistribution. As a conventional indication for coronary revascularization, the Tl score is relatively useful for predicting improvement after revascularization.