To evaluate the safety and possible efficacy of high-dose naloxone for the treatment of acute cerebral ischemia, 38 patients received a loading dose of 160 mg/m2 over 15 minutes followed by a 24-hour infusion at the rate of 80 mg/m2/hr. Nausea and/or vomiting were common side effects. Naloxone was discontinued in seven patients (because of hypotension in one, bradycardia and hypotension in two, myoclonus in one, focal seizures in two, and hypertension in one); all seven patients responded to treatment and no permanent sequelae to naloxone were noted. Twelve of the 38 patients showed early neurologic improvement (by completion of the naloxone loading dose). However, there was no correlation between such a loading dose response and clinical outcome at 3 months. Our experience suggests that naloxone is safe at the dose used, but data for efficacy are inconclusive.