Fentanyl citrate is a synthetic narcotic 1,000 times as potent as meperidine. It produces minimal hemodynamic effects and is characterized by a rapid onset of sedation and analgesia, a relatively short duration of action (approximately 30 to 40 minutes), and rapid reversal with opiate antagonists. These properties make fentanyl and ideal drug for emergency department use. The safety of fentanyl use in an adult ED population has not previously been studied. We retrospectively reviewed the charts of 841 patients who received fentanyl at the University of Cincinnati Center for Emergency Care between January 1985 and June 1988. The study population included 497 (59%) men and 344 (41%) women, with an average age of 33 years. The average dose of fentanyl was 180 μg (range, 25 to 1,400 μm). Six patients (1%) experienced mild side effects including nausea (one), emesis (two), urticaria (one), and pruritis (two). Nine patients (1%) developed more serious complications including six cases (0.7%) of respiratory depression and three cases (0.4%) of hypotension. Two of 183 patients (1%) who received midazolam and two of nine patients (22%) who received haloperidol developed respiratory depression and two of the three patients with hypotension were intoxicated. All of the complications were transient, and none resulted in hospitalization. We conclude the fentanyl is a safe drug for use in the ED. to maximize safety, we recommend careful dosing and titratin, close patient monitoring, and the availability of naloxone hydrochloride and resuscitation equioment. In addition, we suggestt cautious use in the intoxicated patient and in patients receiving other drugs with central nervous system or respiratory depresant activity.