BACKGROUND: If general anesthesia is used for cesarean section, important considerations include minimizing the duration of general anesthesia. One may think that skin incision should be started immediately after endotracheal intubation. If so, intra-operative awareness and perception of pain may occur due to light anesthesia. Allowing skin incision to be started 5 min after intubaton while administering 50% nitrous oxide and isoflurane 0.75%, we investigated the changes of BIS (bispectral index), and Apgar scores. METHODS: The investigation was carried out on 33 full-term ASA 1 or 2 patients underwent elective cesarean section under general anesthesia. If any fetal abnormalities were found, we excluded those cases. Premedication was omitted. After rapid sequence induction with sodium thiopental 4 mg/kg, succinylcholine 1 mg/kg, we made skin incision immediately after intubation in control group (n = 18) and 5 min after intubation in experimental group while administering 50% nitrous oxide and isoflurane 0.75%. Muscle relaxation was maintained with intravenous administration of atracurium 0.5 mg/kg. We measured BIS, mean arterial pressure (MAP), heart rate in 1 min interval from preinduction period to delivery and recorded Apgar scores 1 and 5 min after delivery, skin incision to delivery time and uterine incision to delivery time. And we counted the number of patients whose BIS values had been below 60 and 70 from skin incision to delivery in each group. RESULT: Apgar scores recorded 1 and 5 min after delivery did not show significant differences between control and experimental group. During the periods of abdominal wall traction, uterine incision and delivery, BIS values of experimental group were significantly lower than control group and moreover, tended to remain below 60 while those of control group during the same periods tended to be above 60 (P < 0.05). The number of patients of experimental group, whose BIS values had been below 60 from skin incision to delivery, was twice as much as that of control group (P < 0.05), but in case of BIS value below 70, there was no significant difference between control and experimental group. During the periods of skin incision and abdominal wall traction, the MAP's of experimental group were significantly lower than control group (P < 0.05). In cases of heart rate, skin incision to delivery time and uterine incision to delivery time, there were no significant differences between control and experimental group. CONCLUSION: Allowing the skin incision to be started 5 min after intubation while administering 50% nitrous oxide and isoflurane 0.75%, BIS values remained below 60 from abdominal wall traction to delivery, and anesthetics-induced fetal depression did not occur.