Technetium-99m tetrofosmin is a new myocardial imaging agent with improved handling and kinetic characteristics. The purpose of this study was to compare the ability of planar and SPECT Tc-99m tetrofosmin imaging with Thallium-201 planar data to detect coronary artery disease and individual vessel lesions ( > 50% diameter stenosis). Seventy-two patients with definite or suspected coronary artery disease were included. Sixty-three had angiographic evidence of coronary artery disease, among whom 42 had had a previous myocardial infarction, while 21 had not. The total number of diseased arteries was 111. Patients underwent symptom-limited treadmill or bicycle exercise to similar endpoints. Thallium and tetrofosmin images were analysed separately by consensus reading. Interpretation was made for five standard anatomical regions (anterior, septal, inferior, lateral and apex), classified into four categories (normal, reversible, fixed and mixed defects). Sensitivity and specificity to detect coronary artery disease were 71% and 78% for Thallium-201 vs 68% and 78% for tetrofosmin by planar imaging, and 87% and 89% for tetrofosmin by SPECT. The improved sensitivity of SPECT was confirmed both in patients with and without previous myocardial infarction. The sensitivity to detect individual vessel lesions was improved by SPECT (59% tetrofosmin SPECT vs 50% thallium planar and 51% tetrofosmin planar). Individual vessel lesion detection by SPECT was 50% for the left anterior descending coronary artery, 42% for the left circumflex and 86% for the right coronary artery. This study confirms the value of technetium-99m tetrofosmin as a myocardial imaging agent. Improvements in diagnosis and in evaluating extent of disease can be expected from using SPECT.