Nine of 34 primary hypertensive men with an electrocardiographic (ECG) pattern of left ventricular hypertrophy showed normalization of the repolarization phase following antihypertensive therapy. A study of the left ventricular load both before therapy, and coincident with the reversion to normal repolarization after treatment, was thought to be a useful means for insight into the mechanisms responsible for the ST-T alterations in hypertension. There was no significant difference in the pretreatment values of arterial pressure, heart rate, peripheral resistance, left ventricular work, pressure-time per beat, and tension-time index between those patients who showed ECG improvement and those who did not. Following therapy, the only significant difference (p<0.01) in the hemodynamic pattern between the two groups was the larger reduction of tension-time index in the responder subjects. Improvement of left ventricular function, which occurred in the responders, was one of the main reasons for the greater decrease in tension-time index. The close relation between the reduction of tension-time index, which is known to be the major determinant of the myocardial oxygen consumption, and reversion to normal of the repolarization supports the possibility that, at least in some patients, the ST-T changes in hypertension reflect an insufficient energy supply in relation to the demand brought about by the high levels of cardiac load.