Objective To determine the 95 ％ effective target plasma concentration (EC95) of remifentanil for tracheal tube tolerance during the recovery period from anesthesia following cervical spine surgery.Methods Thirty ASA Ⅰ or Ⅱ patients,aged 18-60 yr,weighing 50-80 kg,scheduled for elective cervical spine surgery under total intravenous anesthesia,were enrolled in this study.Anesthesia was induced with iv injection of propofol,sufentanil and rocuronium.The patients were tracheal intubated and mechanically ventilated.Anesthesia was maintained with iv infusion of propofol and target-controlled infusion of remifentanil.The target plasma concentration (Cp) of remifentanil was set at 4-6 μg/L.BIS value was maintained at 40-60.Infusion of propofol was stopped at the end of surgery.Participants were allocated to a dose of remifentanil by 3-patient cohorts.Six Cps were selected from 1.0-3.5 μg/L before beginning and they were 1.0,1.5,2.0,2.5,3.0,3.5 μg/L.The Cp of remifentanil was 3.0 μg/L in the first cohort.After completion of the trial in each cohort,the posterior probability of each concentration was calculated according to the condition of sedation/analgesia and anterior probability of each concentration.The concentration with the posterior probability closest to 95 ％ was chosen as Cp in the next cohort.The concentration-probability curve was made according to the posterior probability of each concentration,and then EC95 and 95 ％ confidence interval of remifentanil were calculated.Results The EC95 and 95 ％ confidence interval of remifentanil were 2.77μg/L (2.65-2.83 μg/L) for tracheal tube tolerance during the recovery period from anesthesia following cervical spine surgery.Conclusion The EC95 of remifentanil for tracheal tube tolerance during the recovery period from anesthesia is 2.77 μg/L in patients undergoing cervical spine surgery.