Exercise ECGs (bicycle ergometry in recumbency) were obtained in 252 women (aged 20-49 years) without evidence of organic heart disease. In 51 (20%) there was a false-positive change in the ECG with horizontal or descending S-T depression greater than or equal to 1 mm. The frequency of this change increased with increasing age. In group I (20-29 years) it was 5%, in group II (30-39 years) 20%, in group III (40-49 years) 38%. In 34 of the 51 women abnormal repolarisation changes were present even at rest. The S-T depression during exercise in most cases amounted to less than 2 mm and often occurred only on maximum exercise during the first or second minute of the recovery phase. These "ischaemia" changes disappeared in 29 of 41 women after administration of 100 mmol potassium chloride. Nine of 12 women in whom the positive ECG signs persisted after KCl, coronary angiography failed to demonstrate any abnormalities.