BACKGROUND: Significant analgesic synergy is obtained when opioids are combined with dilute local anesthetics, but serious side effects of intraspinal opioid can develope. The purpose of this study was to see how much does additional fentanyl make change of hemodynamics and analgesic dermatome according to variation of local anesthetic concentration. METHODS: Thirty patients were divided into three groups who were receiving epidurally 0.33% bupivacaine 15 ml(group 1), 0.33% bupivacaine 15 ml including fentanyl 100 g(group 2), 0.25% bupivacaine 15 ml including fentanyl 100 g(group 3) at the C7-T1 interspace. We observed mean arterial blood pressure, pulse rate and arterial blood gas analysis to be changed. Evaluation of the onset and duration of analgesic action by pin prick test were taken. Also side effects and complications were checked. RESULTS: Decreases of mean arterial blood pressure was statistically significant between 10 and 120 minutes in group 1, between 10 and 50 minutes in group 2, between 10 and 40 minutes in group 3 after drug administration. Decreases of pH and increases of PaCO2 were statistically significant between 30 and 60 minutes in group 1, between 30 and 120 minutes in group 2, 3 after drug administration. In three groups, number of analgesic dermatome was maximal at 40 minutes after drug administraion. The duration of analgesia in C8 dermatome was 153 29 minutes in group 1, 168 21 minutes in group 2, 131 31 minutes in group 3. Inadvertant dural puncture was developed in one patient. Transient pruritus, nausea/vomiting and solmnolence were developed in group 2, 3. CONCLUSIONS: Three groups provided sufficient analgesia for operation. fentanyl affects on hemodynamics, ventilation but not on number of maximal analgesic dermatome. Also it produces side effects such as, mild pruritus, somnolence, nausea/vomiting.