The purpose of this open, prospective, randomized, comparative study was to examine the effectiveness of atenolol, a cardioselective beta1 blocker, alphamethyldopa, an alpha-adrenergic antagonist, and ketanserin, a serotonin receptor antagonist, in the treatment of 90 patients (N-30 each) with severe chronic hypertension (ChH) during pregnancy or severe pregnancy-induced hypertension, with or without proteinuria in either case.Arterial blood pressure (BP) for each drug group was analyzed at the onset of treatment, weekly for three weeks, and at the end of pregnancy. After one week of treatment a significant drop in BP was observed in the three groups of patients. Thereafter BP remained stable until the end of gestation, when a slight increase in BP was observed, especially in the group of patients treated with ketanserin.No significant difference was observed between the groups in mean birthweight and perinatal morbidity and mortality. No adverse effects from the drugs on the fetus or newborn were observed. No significant difference was observed among the three drugs in their antihypertensive effect. However, given the relatively small numbers of patients studied, definitive statements regarding the relative efficacy and safety of alphamethyldopa, ketanserin and atenolol cannot be made. Thus, additional, larger controlled trials of these agents are required.