Central haemodynamics were studied invasively at rest and during ergometer-bicycle exercise in 77 males with essential hypertension aged 17-66 years and in 33 age-matched normotensives. At the start of the study, resting cardiac index, the heart rate, oxygen consumption (VO2) and mean arterial blood pressure were about 15% higher in those hypertensive patients aged 17-29 years than in the normotensives while the total peripheral resistance index was similar in both groups. During exercise, the stroke index decreased significantly and the total peripheral resistance index increased in the hypertensive group. After 10, and then 20 years, central haemodynamics were restudied in the hypertensive patients. The initially high cardiac index-low total peripheral resistance index pattern was reversed after 10 years. At the 20-year follow-up there was a further fall in the cardiac index and a more marked increase in the total peripheral resistance index at rest as well as during exercise. The study has shown a progressively abnormal haemodynamic pattern over two decades in young subjects with essential hypertension, characterized by a reduced cardiac function and excessive systemic vascular resistance.