Objective To determine the half-effective target plasma concentration(EC50)of remifentanil inhibiting airway response when combined with propofol by TCI in patients undergoing fiberoptic bronchoscopy.Methods Forty ASAⅠorⅡ patients,aged 20-64 yr, undergoing elective fiberoptic bronchoscopy, were randomly divided into 2 groups (n = 20 each).Anesthesia was performed with TCI of remifentanil and propofol in both groups. The target effect site concentration of propofol was 3 μg/ml.The target effect site concentration of remifentanil was determined by up-and-down sequential hial. The target effect site concentration of remifentanil was set at 5 μg/ml in the first patient and the ratio of the target concentrations between the two consecutive patients was 1.1. BIS ≤ 60 was defined as the suitable depth of anesthesia in group A.The airway response≤grade Ⅱ was defined as the suitable depth of anesthesia in group B. The EC50 and 95% confidence interval (CI) required to inhibit the airway response were calculated in the two groups.Results The EC50 and 95% CI of remifentanil required to inhibit the airway response were 4.50μg/L (95% CI 3.88-5.36 μg/L)in group A and 4.10μg/L(95% GI 3.31-5.00 μg/L) in group B. The EC50 of remifentanil inhibiting airway response was significantly higher in group A than in group B. Conclusion The EC50 of remifentanil inhibiting airway response is 4.10 μg/L when combined with propofol by TGI (effect site concentration 3μg/ml)in patients undergoing bronchoscopy. BIS is not a suitable index assessing the depth of propofol-remifentanil anesthesia.