The pharmacokinetics, pharmacodynamics, and clinical uses of fentanyl, sufentanil, and alfentanil are reviewed. The fentanyl derivatives have reduced or eliminated many of the disadvantages of opioid anesthetics, such as incomplete amnesia and undesirable hemodynamic responses to surgery. Fentanyl is 50-100 times as potent as morphine and was the first of the three to be marketed. Sufentanil is even more potent than fentanyl. Alfentanil has the fastest onset of action, followed by sufentanil and then fentanyl. Alfentanil also has the shortest duration of action of the group. Most studies of these agents have been done to assess their role as anesthetics in cardiac surgery. All three provide cardiovascular stability when administered before noxious surgical stimuli, except when given as a single bolus during the induction of anesthesia. All seem to produce adequate anesthesia, particularly when used in combination with nitrous oxide. Because of its short duration of action, alfentanil is preferred for brief procedures or when rapid changes in the level of consciousness are desired. All three agents have also been used for analgesia; epidural administration provides adequate relief of pain. Fentanyl has been formulated as a transdermal patch that seems to provide the same degree of analgesia as a continuous i.v. infusion. Fentanyl has also been formulated as an investigational lozenge that has shown advantages as a preoperative sedative in children. As more is learned about these agents, their perioperative uses for anesthesia, analgesia, and sedation will continue to be refined.