We conducted a randomized clinical trial in which patients with severe preeclampsia between 26-36 weeks of gestation received either nifedipine (10-30 mg sublingually, then 40-120 mg/day orally; N = 24) or hydralazine (6.25-12.5 mg intravenously, then 80-120 mg/day orally; N = 25). Effective control of blood pressure was achieved with nifedipine in 95.8% of subjects and with hydralazine in 68%, a statistically significant difference (P less than .05). Maternal side effects were minor in both groups. Acute fetal distress developed in one nifedipine subject and in 11 treated with hydralazine. Mean prolongation of gestation was 15.5 +/- 10 days with nifedipine and 9.5 +/- 11 days with hydralazine, a difference that did not reach statistical significance (P less than .07). Infants born to women treated with nifedipine were delivered at more advanced gestational ages (34.6 +/- 2.3 versus 33.6 +/- 2.4 weeks; statistically not significant), weighed more (1826 +/- 456 versus 1580 +/- 499 g; statistically not significant), and tended to have fewer, mainly minor, complications. The average number of days spent in the neonatal intensive care unit was significantly lower in the nifedipine group (15.1 versus 32.7 days; P less than .005), leading to an average 31% reduction in total (maternal and neonatal) hospitalization-related charges for each nifedipine-treated pregnancy. We conclude that nifedipine is an effective, convenient, and low-cost treatment for patients with severe preeclampsia, and is not associated with undesirable side effects.