Objective To determine the half-effective target effect-site concentration (EC50) of sufentanil inhibiting responses to insertion of Streamlined Liner of the Pharynx Airway (SLIPA) when combined with propofol given by target-controlled infusion (TCI).Methods Twenty-eight patients,aged 35-55 yr,with body mass index＜30 kg/m2,of American Society of Anesthesiologists physical status Ⅰ or Ⅱ,scheduled for elective hysteroscopic surgery,were selected.Sufentanil was administered by TCI at a concentration for 4 min,and then propofol was given by TCI at a target effect-site concentration of 4 μg/ml.When the patients lost consciousness (bispectral index value＜60) and the corresponding target effect-site concentrations of two drugs were achieved,SLIPA was inserted.Using the up-and-down sequential trial,the target effect-site concentration of sufentanil was determined according to patient's responses to SLIPA insertion.The initial target effect-site concentration of sufentanil was 0.3 ng/ml,and the ratio between the two successive concentrations was 1.1.The EC50 and 95％ confidence interval of sufentanil inhibiting responses to SLIPA insertion were calculated by using Dixon-Mood formula.Results The EC50 of sufentanil inhibiting responses to SLIPA insertion was 0.17 ng/ml,and the 95％ confidence interval was 0.15-0.19 ng/ml.Conclusion When combined with propofol (target effect-site concentration 4 μg/ml) given by TCI,the EC50 of sufentanil inhibiting responses to SLIPA insertion is 0.17 ng/ml.