OBJECTIVE To study how the treatment of severe gestational hypertension affects maternal middle cerebral artery velocimetry. METHODS Prospective, clinical, descriptive study. METHODS John Radcliffe Maternity Hospital, Oxford, England. METHODS Pregnant and puerperal women who required acute or chronic antihypertensive treatment with nifedipine (n = 46) or methyldopa (n = 26), respectively. METHODS Transcranial Doppler ultrasound examinations of maternal middle cerebral arteries were performed before and 45 min after nifedipine; and before and 48 hours after the onset of methyldopa therapy. Blood pressure and heart rate were also recorded. METHODS Clinical and transcranial Doppler changes induced by the antihypertensive medication. RESULTS Blood pressure and middle cerebral artery velocities decreased significantly following both short- and long-acting antihypertensive therapy. Nifedipine-induced changes were more pronounced and uniform than those found after methyldopa (16.7% and 6.4% decrease in middle cerebral artery mean velocity, respectively). The middle cerebral artery mean velocity decrease was independent of changes in the blood pressure or heart rate. CONCLUSIONS Maternal cerebral haemodynamics are influenced by antihypertensive treatment. The reduction of middle cerebral artery flow velocities following administration of nifedipine and methyldopa may suggest that cerebral vasodilatation is occurring, which is consistent with the concept that cerebral vasospasm is present in women with pre-eclampsia. The cerebral vasodilatation could result from a direct effect of the medication on the arteries in question.