The aim of this study was to compare regional perfusion of myocardium measured with Tl-201 and Tc-99m CARDIOLITE in 35 patients with coronary artery disease. All the patients were examined three times. Investigations with Tc-99m CARDIOLITE at stress and rest were performed after twice done injection of dose. Tl-201 was given within 7 days from investigations with Tc-99m CARDIOLITE. All the patients were stress tested according to Bruce's protocol. The radiopharmaceutic was injected at maximal ergometric stress level and then stress was continued for at least one minute. The results of regional perfusion scintigraphy--separately with Tl-201 and Tc-99m CARDIOLITE--were compared in 19 patients with contrast coronarography. Similar sensitivity, specificity and accuracy were obtained for both tracers, 67%, 80%, 71% respectively for Tl-201 and 69%, 86%, 73% for Tc-99m CARDIOLITE. Entire accuracy was obtained in 80% comparisons in segment to segment correlation. Tc-99m CARDIOLITE showed smaller perfusion defect in 9% comparisons and greater in 11%. This findings suggest that both tracers can be used interchangeably.