In this study, tomographic 201Tl washout analysis and coronary angiography were compared in 100 subjects. Seventeen subjects with healthy coronary arteries were used as reference material, on the basis of which the reference ranges for both the total washout of the heart muscle and the regional washout were determined. With angiography as the standard, this material yielded the following sensitivity values for total myocardial washout: 80% for three vessel proximal disease (n = 30), 64% for peripheral three vessel disease (n = 14), 66% for two vessel disease (n = 29) and 71% for single vessel disease (n = 17). Specificity in the reference group was 94%. Sensitivity values for regional washout were 83%, 93%, 59% and 71%, respectively. Stress ECG gave about 10% lower sensitivities. As far as sensitivity is concerned, however, visual assessment of tomographic images proved to be the best single method. In three patients, washout analysis was necessary to reveal evenly distributed ischemia and in seven cases it was essential in order to confirm an uncertain diagnosis; in other words, washout analysis had diagnostic value in 10 of the 100 patients.