This experiment was performed to investigate the ability of naloxone to reverse high dose barbiturate anesthesia or produce cerebrovasodilation or changes in cerebral metabolism in dogs neuronally depressed by high doses of barbiturate. Six dogs were deeply anesthetized with sufficiently high doses of sodium pentobarbital to produce and then maintain isoelectric activity or cerebral silence on the electroencephalogram (EEG). Blood flows were determined using the radioactive microsphere technique both before and after the intravenous bolus injection of naloxone (10 mg/kg), which failed to produce any significant changes in cerebral blood flow, the cerebral metabolic rate of oxygen, cerebrovascular resistance, or EEG activity. Cardiovascular parameters were also essentially unchanged. Naloxone in a dose of 10 mg/kg i.v. produced no changes in the cerebral or systemic circulations or in brain metabolism during high dose sodium pentobarbital anesthesia.