BACKGROUND: To estimate real time concentration of drugs during TIVA is theoretical, but it is not easy and inefficient. To maintain designed target concentration with continuous infusion using methods that account for the multicompartmental pharmacokinetic profile of fentanyl, isoconcentration nomogram is one of the methods. We evaluated the clinical usefulness of the isoconcentration nomogram using two different expected concentration of fentanyl. METHODS: Thirty ASA class I or II adult patients scheduled for spine fusion were randomly allocated into two groups according to 1.5 or 3 ng/ml of expected fentanyl concentration. Using isoconcentration nomogram, fentanyl concentration was adjusted and the propofol concentration was fixed to 3.5 g/ml according to Prys-Roberts method. Vital signs were titrated using variable flow rate of propofol. Fentanyl and propofol were discontinued 15 min before the end of operation. And, IV-PCA using fentanyl were applicated for postoperative pain control. The dosage of propofol and fentanyl, recovery time of consciousness and orientation were checked. Also, first buttoning time and 24hr fentanyl dosage in IV-PCA were checked. RESULTS: Average flow rate of propofol used were 7.5 1.2 mg/kg/hr in group 1, 5.7 1.1 mg/kg/hr in group 2 which was significantly lower than group 1 (p<0.05). Spontaneous eye opening and recovery of orientation was delayed 1.8 times in group 2. First buttoning time and 24hr fentanyl requirement for postoperative pain control using IV-PCA was delayed by 2 and decreased 60% in group 2, respectively. CONCLUSIONS: Isoconcentration nomogram was useful tool to control the expected concentration of fentanyl during TIVA and postoperative pain control using fentanyl IV-PCA.