Objective To determine the median effective dose(ED50)of etomidate inhibiting responses to endotracheal intubation when combined with dexmedetomidine in the patients with obstructive jaundice. Methods American Society of Anesthesiologists physical status Ⅱ or Ⅲ patients with obstructive jaundice,aged 45-63 yr,with body mass index of 18-30kg/m2,scheduled for elective operations under general anesthesia,were divided into control group(group C)and dexmedetomidine group(group D)using a random number table. At 15min before induction of anesthesia,normal saline 0.1 ml/kg was infused intravenously in group C,and dexmedetomidine 0.4 μg/kg was infused intravenously in group D. Anesthesia was induced with midazolam 0.05 mg/kg,fentanyl 4 μg/kg,etomidate and cisatracurium 0.15 mg/kg. The ED50 of etomidate was determined using Dixon′s up-and-down method. Etomidate was injected intravenously at the initial dose of 0.2 mg/kg in the first patient in each group. Each time the dose increased/decreased in the next patient according to whether or not the increase in mean arterial pressure and/or heart rate ≥ 20% of the baseline value within 3min after endotracheal intubation. The ratio between the two successive doses was 1.1. The number of patients in whom inhibition was effective or ineffective was recorded,and the ED50 and 95% confidence interval of etomidate inhibiting responses to intubation were calculated using Probit analysis. Results The ED50 (95% confidence interval)of etomidate inhibiting responses to intubation was 0.185(0.162-0.201)mg/kg in group C,the ED50(95% confidence interval)of etomidate inhibiting responses to intubation was 0.129(0.093-0.143)mg/kg in group D,and there was significant difference between the two groups(P<0.05).Conclusion When combined with dexmedetomidine,the ED50 of etomidate inhibiting responses to endotracheal intubation is 0.129 mg/kg in the patients with obstructive jaundice.