Two hundred and fifteen patients with previous myocardial infarction were investigated between four and six months after the acute episode by computer assisted 12 lead exercise electrocardiography. Thirty-six (17%) out of this group showed ST segment elevation over the infarct zone, reflected by leads presenting with "QS" configuration. They were further investigated by serial thallium-201 scintigraphy, coronary arteriography, and left ventricular angiography. All showed left ventricular wall motion abnormalities and 89 per cent were diagnosed to have left ventricular "aneurysm" (dyskinesia and akinesia). In a further patient with a posterior aneurysm, the exercise-induced ST elevation could only be detected by using an oesophageal lead. We suggest that these changes reflect severe underlying left ventricular wall motion abnormalities in the presence or absence of reversible myocardial ischaemia. The mechanism of ST segment elevation in this situation, occurring in leads with a "QS" configuration, may be mechanical in the majority of the patients rather than due to reversible myocardial ischaemia.