Abstract Systemic hæmodynamic changes were studied twice in thirteen patients with essential hypertension: (i) before treatment, and (ii) after 1 year of good control of blood pressure, 4 weeks after stopping diuretics and 1 week after stopping other drugs. At each study observations were made before and during autonomic blockade to assess the reversibility by treatment of non-autonomic (humoral or structural) factors influencing hæmodynamics. After 12 months' treatment mean arterial blood pressure (MAP) was 15·5 mm Hg lower (p<0·05), cardiac index (CI) 25% higher (p<0·05), and total peripheral resistance index (TPRI) 31% lower (p<0·01) before autonomic block than the corresponding pre-treatment values. After autonomic block similar differences were observed in all variables, and the non-autonomic component of TPRI had fallen into the range found in normotensive subjects. Patients remained off therapy after the second study and blood-pressure returned to pretreatment levels by 1-4 months in twelve out of thirteen patients. The findings suggest that one year's successful treatment of mild essential hypertension almost completely corrects hæmodynamic variables, including "non-autonomic" total peripheral resistance.