We determined the minimal alveolar concentration (MAC) of sevoflurane inducing an isoelectric EEG in 50 of adult subjects (MACie). We included 31 middle-aged subjects; 30 subjects finished the study protocol and received sevoflurane at preselected concentrations according to a modified Dixon up-and-down design starting at 1.7 vol with 0.2 vol steps size. General anaesthesia was induced and maintained with sevoflurane; tracheal intubation was facilitated with cisatracurium. After a period of 30 min before skin incision, the state of isoelectric EEG was considered as significant when a burst suppression ratio of 100 lasted for 1 min. The haemodynamic responses to skin incision and the vasopressor requirement to maintain stable haemodynamic status were also analysed according to the EEG state. MACie was 3.5 (95 confidence interval, 3.43.7) in middle-aged subjects. When compared with subjects not in isoelectric EEG state, subjects in isoelectric EEG state received more phenylephrine to maintain stable haemodynamics (10 of 10 compared with 7 of 20 subjects, P0.001) and experienced less sympathetic responses to skin incision (1 of 10 compared with 11 of 20 subjects, P0.024). MACie for sevoflurane was 2.1 times MAC for immobilization in phenobarbital premedicated middle-aged adults. Sevoflurane-induced isoelectric EEG state is associated with significant cardiovascular depression but reduced haemodynamic responses to skin incision.