The cochlear and cerebral blood flow were simultaneously measured with the microsphere method in albino rabbits before and after administration of prazosin (0.5 mg/kg body weight) and before and during an increase in intracranial pressure (ICP) and intraco-chlear pressure. Increments in ICP were induced by intracranial infusion of Ringer solution prewarmed to body temperature. The increments were accompanied by an intravenous administration of prazosin to abolish the Cushing effect. The cochlear blood flow was unaffected by the intravenously administered prazosin. A decrease was found when the perfusion pressure of the cochlear, i.e. mean arterial blood pressure minus ICP fell below 5 kPa.