Prazosin (Minipress; Pfizer), the first purely alpha-blocking antihypertensive agent, was used to treat 22 pregnant patients with moderately severe hypertension (diastolic blood pressure persistently above 95 mmHg at gestational ages ranging from 18 to 33 weeks). Prazosin was used because it is a postsynaptic alpha-blocking agent producing no direct tachycardia or renin stimulation and because its action in producing visceral vasodilation might improve uteroplacental perfusion. Oxprenolol (Trasicor; Ciba), a beta-blocking agent with intrinsic sympathomimetic activity, was added to the prazosin regimen in 12 cases. In this group pregnancy was prolonged for an average of 32 days and 10 infants survived the neonatal period. Fetal loss, mainly due to abortion, was high in the patients who had significant proteinuria, and it was not possible to prolong the pregnancy in these cases. There were no significant maternal, fetal or neonatal side-effects attributable to this combined alpha- and beta-blocking therapy, which may have both theoretical and practical advantages over other current therapies.