Objective To compare the efficacy and safety of remifentanil and fentanyl in patients undergoing a modified radical mastectomy or total hysterectomy.Methods Fifty-four patients were evenly randomised into remifentanil group and fentanyl group. Anesthesia was induced by propofol (1-2 mg/kg) and either remifentanil (2μg/kg) or fentanyl (2. 5 μg/kg), and was maintained with inhalation of nitrous oxide in oxygen (2:1) and continuous infusion of either remifentanil (0. 2μg·kg-1·min-1) or fentanyl (0. 03μg·kg-1·min-1).Results The number of patients exhibiting light anesthesia responses in the remifentanil group during intubation and the maintenance of anesthesia was significantly less than that in the fentanyl group. Both systolic and diastolic blood pressures in the fentanyl group were significantly higher than those in the remifentanil group during intubation, skin incision, maintenance of anesthesia and extubation. The time to opening eyes on command and the time for extubation after surgery was co Objective To compare the efficacy and safety of remifentanil and fentanyl in patients undergoing a modified radical mastectomy or total hysterectomy. Methods Fifty-four patients were evenly randomized into remifentanil group and fentanyl group. Anesthesia was induced by propofol (1-2 mg / kg) and either remifentanil (2 μg / kg) or fentanyl (2.5 μg / kg), and was maintained with inhalation of nitrous oxide in oxygen (2: 1) and continuous infusion of either remifentanil (0.2 μg · kg-1 · min -1) or fentanyl (0. 03 μg · kg-1 · min-1). Results The number of patients exhibiting light anesthesia responses in the remifentanil group during intubation and the maintenance of anesthesia was significantly less than that in the fentanyl group. Both systolic and diastolic blood pressures in the fentanyl group were significantly higher than those in the remifentanil group during intubation, skin incision, maintenance of anesthesia and extubation. The time to opening eyes on command and the time for extubation af ter surgery was co