Correlations between endocrine and cardiological findings were investigated in 106 patients with catecholamine-secreting tumours during the florid phase of their illness. Endocrine data showed an elevation of urinary catecholamine or vanillylmandelic acid excretion in all but one subject. Hypertension was found in 78%, symptoms of coronary heart disease in 26% and arrhythmias in 20% of the patients. Twelve per cent of the patients came to the hospital with heart attacks, 7% with acute left heart failure and 6% with myocardial infarction. At admission electrocardiograph (ECG) analysis showed a sinus rhythm in 98%, tachycardia > 100 min-1 in 14% and bradycardia < 60 min-1 in 10%. In 16% of the ECGs cQT was increased, in 17% the ST segment was lowered and in 37% abnormal T waves occurred. Indices of myocardial hypertrophy such as the Sokolow index, the modified Romhilt-Estes score and the Murphy score were raised in 29%, 19% and 38% respectively. In 23 of 51 (45%) patients echocardiography showed left ventricular hypertrophy, in 16% mitral valve insufficiency and in 24% disturbances of contractility. Comparison of cardiac and endocrine parameters confirm in vitro and animal studies indicating that, in particular, the alpha-mimetic noradrenaline (NA) has deleterious effects on the cardiovascular system. Urinary NA, but not adrenaline or dopamine, excretion was significantly higher in constantly hypertensive than in normotensive patients and associated with an elevation of the Sokolow index and the Romhilt-Estes score. Both indices and plasma NA were higher in patients with myocardial hypertrophy and we found a significant correlation between the Romhilt-Estes score and NA excretion.