Nine anesthetized, artificially ventilated, term newborn beagle puppies were given phenylephrine hydrochloride intravenously while systemic arterial, carotid arterial, and jugular venous blood pressures, and carotid arterial blood flow were monitored. Systemic blood pressure rose within seconds from a mean of 53.68 +/- 1.10 mm Hg to a mean of 81.92 +/- 5.14 mm Hg. Hypertension was maintained for up to one hour in each animal. Four of the nine pups had intraventricular hemorrhages that were visible to gross inspection at autopsy, and seven of the nine pups had subependymal hemorrhages. The blood pressures produced in these animals were within the range of those seen in premature infants. Thus, moderate, rapidly induced systemic hypertension may be a cause of intraventricular hemorrhage in the premature human newborn infant.