The prognostic value of thallium-201 imaging in patients with unstable angina is not well established. Forty consecutive patients with unstable angina who had responded to medical therapy underwent predischarge symptom-limited exercise testing and 39 of them underwent exercise thallium-201 imaging, on average 3 days after the exercise test. Exercise echocardiography was performed in 36 of these patients in conjunction with the predischarge exercise test. Patients with previous myocardial infarction, coronary revascularization, left bundle branch block and dilated cardiomyopathy were not included in the study. An echocardiographic wall-motion score index was derived by analyzing left ventricular regional wall motion. During a follow-up period of 30 +/- 6.4 months, 3 patients had a non-fatal myocardial infarction and 20 required revascularization because of a recurrence of severe medically refractory angina. Univariate predictors of cardiac events (non-fatal myocardial infarction or a need for revascularization) during follow-up included ST-depression during exercise, positive exercise echocardiography, a low exercise wall-motion score index, the presence of thallium-201 redistribution and the number of myocardial segments with thallium-201 redistribution. However, stepwise logistic regression analysis revealed that the presence of thallium-201 redistribution was the only significant non-invasive predictor (P < 0.005) of a cardiac event among patients who underwent predischarge exercise testing and exercise thallium-201 imaging. Among patients undergoing exercise echocardiography and exercise thallium-201 imaging, the number of segments with thallium-201 redistribution was the only significant predictor (P < 0.0005) of future cardiac events.(ABSTRACT TRUNCATED AT 250 WORDS)