1. Cardiac output, oxygen consumption, total blood volume and mean circulatory transit time were investigated at rest in men with sustained essential hypertension in comparison with normal subjects of the same age and sex.
2. In normal subjects and in patients with hypertension, oxygen consumption was positively correlated to cardiac output. In hypertensives, the slope of the curve was significantly shallower with an increase in arteriovenous oxygen difference.
3. Oxygen consumption in both populations was negatively correlated with mean circulatory transit time but not with total blood volume.
4. In normal subjects, mean circulatory transit time and arteriovenous oxygen difference were positively correlated. The correlation was not significant in hypertensive patients.
5. The study suggests important abnormalities in the transport and cost of energy in erythrocytes of patients with sustained essential hypertension.