We studied whether changes in cerebral blood-flow velocity occur during the respiratory-distress syndrome and whether, if present, they are related to the subsequent occurrence of intraventricular hemorrhage. Fifty infants weighing less than 1500 g at birth who required mechanical ventilation for the respiratory-distress syndrome were studied from the first hours of life. Blood-flow velocity in the anterior cerebral artery was measured at the anterior fontanel by means of the Doppler technique. At 12 hours of age, the infants had blood-flow velocity patterns that were either stable or fluctuating and that reflected the patterns of simultaneously recorded blood pressure. Intraventricular hemorrhage subsequently developed in 21 of 23 infants with the fluctuating pattern (in most of them, within the next 24 hours), but in only 7 of 27 infants with the stable pattern. Preliminary data suggest that the cerebral hemodynamic fluctuations are related to the respiratory disease and particularly to the mechanics of respiration. We conclude that the fluctuating pattern of cerebral blood-flow velocity in infants with the respiratory-distress syndrome indicates an extreme risk of the development of intraventricular hemorrhage and may represent a major and potentially preventable etiologic factor.