We studied the effect of mild hypothermic cardiopulmonary bypass (30 degrees C) on the EEG Bispectral Index in 10 patients undergoing elective CABG. BIS was recorded at 11 event-related time points during the procedure. After a significant decrease at the induction of anaesthesia, BIS was not further modified during the procedure. BIS was neither affected by surgical stimulation nor by CPB and mild hypothermia. We conclude that we did not find any reason to preclude the use of BIS to assess the hypnotic effects of anaesthetics during normothermic or mild hypothermic CPB.