Objective To compare the efficacy of different target concentrations of etomidate in combination with midazolam,fentanyl and rocuronium used to induce anesthesia for tracheal intubation.Methods Eighty ASA Ⅰ or Ⅱ and Mallampati Ⅰ or Ⅱ patients of both sexes,aged 25-50 yr,weighing 57-76 kg,scheduled for elective non-cardiac surgery under general anesthesia,were randomly allocated into 4 groups according to the target effect-site concentration of etomidate (n =20 each) ∶ 0.5 μg/ml group (group E0.5),0.7 μg/ml group (group E0.7),0.9μg/ml group (group E0.9) and 1.1 μg/ml group (group E1.1).The patients were unpremedicated.Anesthesia was induced with midazolam 0.05 mg/kg,fentanyl 3 μg/kg,rocuronium 0.6 mg/kg and etomidate given by target-controlled infusion.When the effect-site concentration of etomidate reached 0.5,0.7,0.9 or 1.1 μg/ml,endotracheal intubation was performed.Auditory evoked potential index was recorded before induction of anesthesia (baseline),immediately before intubation,during insertion of the laryngoscope,and at 1,3 and 5 min after intubation.Myoclonus,injection pain,the requirement for vasoactive agents and burst suppression (BS) were recorded during induction of anesthesia.Results Compared with group E0.5,the requirement for urapidil was significantly decreased in group E0.7,the requirement for esmolol and urapidil was significantly decreased and the incidence of BS was increased in group E0.9,the requirement for esmolol and urapidil was significantly decreased,and the requirement for atropine and ephedrine and incidence of BS were increased in group E1.1 (P ＜ 0.05).The incidence of BS was significantly higher in group E0.9,and the requirement for atropine and incidence of BS were significantly higher in group E1.1 than in group E0.7 (P ＜ 0.05).The incidence of BS was significantly higher in group E1.1 than in group E0.9 (P ＜ 0.05).There was no significant difference in auditory evoked potential index and incidences of myoclonus and injection pain among the four groups (P ＞ 0.05).Conclusion The optimum target concentration of etomidate is 0.7μg/ml when combined with midazolam,fentanyl and rocuronium used to induce anesthesia.