The long-term effects of metoprolol monotherapy, 100 mg b.i.d., for 16-18 months, were investigated in 8 previously untreated essentially hypertensive patients (resting blood pressure greater than 155/95 mmHg) and echocardiographic evidence of left ventricular hypertrophy (LVH) (left ventricular mass by Penn Cube formula greater than 215 g). Echocardiographic studies, according to the American Society of Echocardiography recording techniques and measurements criteria, were performed before starting treatment and at the end of follow-up. Metoprolol induced a decrease in systolic and diastolic blood pressure and heart rate, accompanied by a reduction of interventricular septum and posterior wall thickness (from 1.21 cm to 1.10 cm, and from 1.15 cm to 1.06 cm, respectively), left ventricular mass index and mean wall stress. All these changes were significant (p less than 0.01). Cardiac index decreased from 3017 ml/m2 to 2632 ml/m2 (p less than 0.01), mostly because of the reduction in the heart rate. In fact, stroke index, ejection fraction and fractional shortening all slightly increased during treatment in respect to pre-treatment values. Plasma renin activity fell from 1.45 ng/ml/h to 0.81 ng/ml/h (p less than 0.01), whereas both plasma noradrenaline and adrenaline concentration at rest did not change. Results indicate that in essentially hypertensive patients who have already developed LVH as a consequence of the hypertension, a long-term metoprolol therapy can successfully induce a reversal of LVH together with an effective blood pressure control, without noticeable adverse effects of changes in cardiac performance.