In 14 essential hypertensive patients, aged 26-59 years, blood pressure, left ventricular mass index (LVMI), systolic function (M-mode echo, two-dimensionally guided), post-ischaemic 'maximal' forearm blood flow (strain gauge venous occlusion plethysmography), plasma renin activity, plasma catecholamines and aldosterone were measured before and after 6 and 12 months of treatment (eight patients were given captopril, 100 mg/day, + hydrochlorothiazide 25 mg/day in five patients, and six patients were given nitrendipine, 20 mg/day, + atenolol 50 mg/day in four patients). Minimal vascular resistance (mean blood pressure/peak forearm blood flow) was taken as an index of arterial structural changes. After 6 months of treatment significant reductions in blood pressure (P less than 0.001), LVMI (P less than 0.001) and minimal vascular resistance were observed. After 12 months of treatment blood pressure, LVMI and minimal vascular resistance were further reduced. The LVMI was normalized in nine cases and the minimal vascular resistance in two cases only. Aldosterone and plasma catecholamines did not change, whereas plasma renin activity was increased during captopril only. Before and during treatment the left-ventricular shortening fraction in relation to end-systolic stress in each patient at rest, and at peak of handgrip and cold pressor tests, fell within the 95% confidence limits of correlation obtained in normals. Thus, in essential hypertensives long-term treatment can induce normalization of LVMI before complete regression of arterial structural changes in the forearm. Left ventricular systolic function is preserved after normalization of LVMI, both at rest and during stress.