Post-exercise ECGs and coronary arteriograms were compared in 180 unselected patients. Coronary-artery stenosis had been diagnosed correctly by arteriography in 94% of cases. In 60% this was also possible from the resting ECG (signs of myocardial infarction), while in the remaining 34% only the exercise ECG was positive. Post-exercise ECG changes are thus an important and largely specific means of diagnosing coronary-artery stenosis.