1. A double-blind cross-over evaluation of the anti-hypertensive effect of metoprolol vs placebo was carried out in a series of twenty-three patients with mild or moderate essential hypertension who were receiving 25 mg of chlorthalidone daily as their basic treatment. An individually determined dose of metoprolol (75–300 mg) was used.
2. Metoprolol, as compared with placebo, produced a statistically significant reduction of blood pressure, both in supine and standing positions.
3. During the double-blind cross-over study mild side effects were more common at the beginning of metoprolol/chlorthalidone treatment than during placebo/chlorthalidone, but these tended to diminish or disappear with time.
4. Metoprolol in combination with chlorthalidone appears to be an effective and well-tolerated treatment for mild and moderate hypertension in patients not responding to chlorthalidone alone.