The yield of exercise thallium-201 scintigram was studied in a group of 101 patients with suspected coronary artery disease or with a history of an old acute myocardial infarction. The thallium perfusion imaging was performed with planar technology and was interpreted visually. Its results were compared with conventional exercise testing and the results of a coronary arteriography performed within 30 days. Global sensitivity for conventional exercise testing was 60.4%, which increased to 78.2% with the thallium study. Specificity was raised from 47.2 to 84.8%. In patients with one, two or three vessel disease, thallium scintigram was abnormal in 95.1%, 96.6% and 100% respectively (NS).