BACKGROUND: The incidence of intraoperative awareness is known to be high in cardiac surgery using cardiopulmaonary bypass, and there is a tendency to use more anesthetics to maintain anesthesia without recall. We investigated the usefulness of the bispectral index monitor in reducing the amount of anesthetics without intraoperative awareness. METHODS: Forty patients scheduled for elective coronary artery bypass graft surgery under cardiopulmonary bypass were randomly allocated into two groups. In the control group, systemic blood pressure was a main indicator to contol the infusion rate of propofol and fentanyl. Infusion rate of propofol and fentanyl were controlled by the bispectral index in the BIS group. A post- anesthetic interview relating to intraoperative awareness was performed on the second postoperative day by a research assistant. RESULTS: The average flow rate of propofol (control group; 0.137+/-0.012 mg/kg/min, BIS group; 0.110+/-0.003 mg/kg/min, P<0.01) and fentanyl (control group; 6.485+/-0.413mug/kg/h, BIS group; 4.321+/-0.5mug/kg/h, P<0.01) were significantly different between groups. The postoperative extubation time was 6.8+/-1.9 h in the control group and 5.3+/-2.3 h in the BIS group (P<0.05). The average BIS was 43.1+/-5.6. No subjects showed positive results in the intraoperative awareness test. CONCLUSIONS: Intraoperative monitoring of the bispectral index in patients undergoing cardiopulmonary bypass for coronary bypass surgery reduced requirement of anesthetics without intraoperative awareness.