In 101 hypertensive gravidae the selective β-blocking agent metoprolol alone or in combination with hydralazine has been used. The effects of the mother and fetus have been compared with those of 97 hypertensive gravidae treated with hydralazine. In both groups a small dose of a thiazide was added. Perinatal mortality was lower in the metoprolol group (2.0%) than in the hydralazine group (8.0%). The rate of fetal growth retardations also was lower when using metoprolol (11.7 and 16.3%, respectively). No abnormal effects of the (β-blocker was noticed on the fetus.