The calcium antagonist, nifedipine, was given orally to 21 women with acute episodes of severe hypertension during pregnancy or in the puerperium. A rapid and significant fall in blood pressure by an average of 26/20 mmHg was seen at 20 min after administration. The hypotensive effect was not significantly enhanced in those women already taking medication to lower the blood pressure. The principal side effects were headache and cutaneous flushing. No adverse fetal effects were detected. This is the first study of the use of this drug to control hypertension in pregnancy. The apparent efficacy of nifedipine justifies its further investigation in controlled trials.