OBJECTIVE: To determine the prognostic role of thallium-201 imaging compared with that of exercise electrocardiography in patients with acute myocardial infarction treated by thrombolysis. DESIGN: Patients who remained free of adverse cardiac events six weeks after myocardial infarction had stress and rest 201TI imaging and exercise electrocardiography and were followed up for 8-32 months. Adverse cardiac events (death, reinfarction, unstable angina, and congestive heart failure) were documented. SETTING: Large district general hospital, Middlesex. SUBJECTS: 100 consecutive male and female patients who were stable six weeks after thrombolysis for myocardial infarction. MAIN OUTCOME MEASURES: Prediction of occurrence of adverse cardiac events after myocardial infarction by exercise cardiography and 201TI myocardial perfusion imaging. RESULTS: Reversible ischaemia on 201TI imaging predicted adverse cardiac events in 33 out of 37 patients with such events during follow up (hazard ratio 8.1 (95% confidence interval 2.7 to 23.8), P < 0.001). Exercise electrocardiography showed reversible ischaemia in 33 patients, of whom 13 had subsequent events, and failed to predict events in 24 patients (hazard ratio 1.1 (0.56 to 2.2), P = 0.8). CONCLUSION: 201TI imaging is a sensitive predictor of subsequent adverse cardiac events in patients who have received thrombolysis after acute myocardial infarction, whereas exercise electrocardiography fails to predict outcome.