The occurrence of neurologic abnormalities is described in a series of nine infants with chronic hypertension, in whom antihypertensive therapy decreased BP markedly and for a prolonged period, although to levels often within the normal range. All infants had mean systolic BPs greater than 113 mm Hg and elevated renin values to a mean of 134 +/- 128 ng/mL/h. Antihypertensive therapy, such as captopril, an inhibitor of angiotensin I-converting enzyme, consistently lowered the systolic BP by 20% from baseline per dose. However, the nine infants exhibited a total of 17 episodes of striking decreases in systolic BP of greater than 40% from baseline; the markedly decreased systolic BP values were usually within the normal range for corrected age. Seven of the 17 episodes were characterized by marked decrease in systolic BP, ie, decreased by 57% +/- 10%, and were prolonged, ie, remained at the lower values for 17 +/- 6 hours despite therapeutic interventions. These seven episodes were accompanied by oliguria (urine output less than 1 mL/kg/h) and neurologic abnormalities (ie, seizures). In the remaining ten episodes, the systolic BP decreased by 50% +/- 8%, but the decreases were relatively brief, ie, remained at the lower values for 2.8 +/- 2 hours. These briefer episodes were not accompanied by renal or neurologic signs. These data indicate a particular vulnerability of the cerebral and renal circulation in premature infants with chronic hypertension to decreases in systolic BP to levels that would otherwise be considered in the normal range. The findings suggest that adaptive responses in both cerebral and renal blood flow are altered by chronic hypertension in such infants.(ABSTRACT TRUNCATED AT 250 WORDS)