Nine patients with suspicious repolarization (ST-T segment) changes in the ECG were further investigated. Each had ten different additional ECG tests (after various degrees of exercise, and orciprenaline, amylnitrite, glucose, potassium chloride, and propranolol injections). The ECG changes became normal in all patients, orciprenaline and propranolol injection providing optimal results. Clinical investigation, left-heart angiocardiography and coronary angiography were normal in all. The questionably abnormal repolarization distrubances were, therefore, judged to be benign. As both beta-stimulation and beta-blockade normalized the ECG it can be safely assumed that the ECG changes were induced by autonomic nervous system factors. Cardiac catheterization appears, therefore, not indicated in each case and a potential iatrogenic heart disease can be avoided by relatively simple means.