Biphasic thallium-201-myocardial imaging was performed in 100 patients undergoing coronary angiography. The images were obtained in several views after the administration of dipyridamole (0.50 mg/kg body weight) and 4 hours later. 24 patients had normal coronary arteries or insignificant stenoses, in 74 patients a 70-percent or greater stenosis of one or more coronary arteries was present. 55 transmural myocardial scars were diagnosed by left ventriculography in 53 patients. The described method showed a sensitivity of 93 percent and a specificity of 96 percent in the detection of patients with significant coronary artery stenoses. Irreversible perfusion defects were found in 91 percent of myocardial scars, in additional 7 percent the scintigraphic defects were reversible. In patients with multivessel disease and transmural infarctions, only one third of non-infarction-related stenoses were recognized. The number of angiographically stenotic coronary arteries could be determined scintigraphically only in a minority of the cases. The regional sensitivity in the assessment of LAD and right coronary artery stenoses was higher than for the left circumflex artery (75%, 80%, and 48% resp.), the specificity was equally high for all three vessels (96%, 99%, 100%).