The usefulness of thallium-201 (Tl-201) exercise myocardial scintigraphy in identifying patients with multivessel coronary artery disease (MVCAD) and residual jeopardized myocardium after myocardial infarction (MI) was evaluated in 32 patients 3 weeks after MI. All patients underwent 1) limited multilead submaximal treadmill testing, 2) thallium-201 (Tl) myocardial scintigraphy at end-exercise and at rest, and 3) coronary and left ventricular angiography. Tl-201 perfusion defects were categorized as either reversible (ischemia) or irreversible (scar). The conventional exercise test was designated positive if there was ST depression ≥ 1mm and/or angina. Jeopardized myocardium (JEP) was defined angiographically as a segment of myocardium with normal or hypokinetic wall motion supplied by a significantly stenotic major coronary artery. MVCAD was defined as two or more significantly stenotic arteries. 'Significant' coronary stenosis was categorized as either 50-69% diameter narrowing or ≥70% diameter narrowing, thereby yielding, respectively, two subgroups each of jeopardized myocardium (JEP-50 and JEP-70) and MVCAD (MV-50 and MV-70). Clinical findings of angina, heart failure or ventricular arrhythmias during the late convalescent period after MI occurred in four of 10 patients (40%) with MV-50, five of 16 (31%) with MB-70, four of 10 (40%) with JEP-50 and five of 18 (28%) with JEP-70, and thus were insensitive for detecting MVCAD and JEP. Reversible ischemia and/or a positive conventional exercise test occurred in five of 10 patients (50%) with MB-50, 13 of 16 (81%) with MV-70, four of 10 (40%) with JEP-50 and 15 of 18 (83%) with JEP-70. All eight patients with both Tl-201 reversible ischemia and a positive conventional exercise test had JEP-70. In 30 of 31 patients (97%) with angiographic asynergy, Tl-201 scar was detected. No complications were associated with exercise testing. Thus, 3 weeks after MI, Tl-201 exercise myocardial scintigraphy is a safe, useful, noninvasive tool for identifying patients with MVCAD and residual JEP and is much more reliable than clinical findings during convalescence after MI.