Thallium 201 exercise redistribution planar myocardial perfusion scan using semiquantitative technique was performed in 80 symptomatic patients undergoing coronary angiography. Out of the 240 vessels studied by angiography, more than 70% luminal narrowing was detected in 87 vessels, borderline stenosis was found in 49 arteries and the remaining 104 vessels were normal. Thallium scan correctly identified the significant stenosis in 76 vessels and the absence of stenosis in 102 vessels. In addition, perfusion abnormality was found in relation with 21 vessels of borderline stenosis. The sensitivity and specificity of Thallium scan were estimated as 92% and 95% for left anterior descending artery (LAD), 79% and 98% for left circumflex artery (LCX), 88% and 100% for right coronary artery (RCA) and 87% and 98% for all coronary arteries combined together (ACA).