Central hemodynamics were studied invasively (blood pressure intra-arterially and cardiac output by dye-dilution method) at rest and during exercise in men with essential hypertension and in age-matched normotensive controls. At the start of the study, resting cardiac index, heart rate, oxygen consumption, and mean arterial pressure were approximately 15% higher in those hypertensive patients aged 17-29 years than in normotensive subjects, whereas total peripheral resistance index was similar in both groups. During exercise, the stroke index was reduced and total peripheral resistance index was increased in the hypertensive group. After 10 and then 20 years, central hemodynamics were restudied in the hypertensive patients. The initially high cardiac index/normal total peripheral resistance index pattern changed to a low cardiac index/high resistance pattern at 10- and 20-year follow-up. In 25 patients initially aged 40-49 years, treatment with diuretics, beta-blockers, or a combination of the two normalized diastolic pressure. In spite of adequate blood pressure control, a marked increase in total peripheral resistance and fall in cardiac index and stroke index were also seen in this age group treated over 20 years. The study has shown a progressively abnormal hemodynamic pattern over two decades in patients of different ages with essential hypertension.