BACKGROUND: The last two decades have seen an increase in the incidence of cesarean section. Spinal anesthesia has been popular in cesarean delivery because of the ease and effectiveness, as well as the rapidity in estabilishing adequate levels of analgesia. The clinical effects of subarachnoid administeration of preservative-free fentanyl were assessed in 30 healthy women who underwent cesarean section with spinal anesthesia using 0.5% hyperbaric bupivacaine. METHODS: Sixty parturients were allocated to group I; bupivacaine (n=30) only and group II; bupivacaine/fentanyl mixture (n=30) in random order. The dose of bupivacaine varied from 9~10 mg depending on the patients height. Maximum level of sensory blockade, time to reach T4 level, incidence of hypotension, time to get complete motor recovery, perioperative analgesic effect and complications were evaluated. RESULTS: There were no differences in maximum level of analgesia, time to reach T4 level and to get complete motor recovery, and incidence of hypotension between two groups. However, duration of analgesia was longer in group II with the bupivacaine/fentanyl mixture (191.9 +/- 77.6 min) than in group I with the bupivacaine alone (74.2 +/- 30.8 min). Spinal anesthesia was excellent in 100% of the fentanyl mixture group but in 80% of the bupivacine only group. CONCLUSION: 0.5% hyperbaric bupivacaine mixed with 25 g fentanyl provided improved perioperative analgesia without affecting the onset of sensory blockade and duration of motor blockade.