Early ECG exercise tests (EET) and ambulatory ECG monitoring (AEM) were performed in 42 patients surviving AMI in order to determine the sensitivity of the two methods for detecting ST-segment deviation and arrhythmias. 23 patients had ST changes during EET and AEM. Of them, 21 patients had ST changes induced by EET and 10 were recorded by AEM. The more the ECG leads used for monitoring during and after EET, the higher the percentage of patients with ST changes will be. There were 2 cases with ST changes found in AEM only. All the 6 patients who had ST elevations during EET had an anterior infarction and echocardiograms did show that they had left ventricular aneurysms or abnormal ventricular wall movement. AEM recorded ventricular premature beats (VPBs) in 37 cases (88.0%), while EET induced VPBs in 8 patients. The 42 patients were followed up for an average time of 6 +/- 1.7 m. (3.4 to 9.3 m.) Cardiac death occurred in 2 cases. One of them had horizontal ST depression of 3 mm during EET, the other had a negative EET but multifocal VPBs during AEM. It is concluded that for detecting ST changes EET is more sensitive than AEM, while VPBs are more frequently found in AEM than in EET. The authors are of the opinion that for better, prediction of the prognosis of patients after AMI, it is preferable to have early EET in combination with AEM.