Abstract： Background Although etomidate is associated with very few cardiovascular side-effects and minimal histamine release, it has a less inhibitory effect on the pharyngolaryngeal reflex. Hence, blunting the responses to endotracheal intubation is more dependent of opioids for etomidate-based anesthetic induction. This prospective, randomized, double-blinded study was designed to investigate the effects of low dose remifentanil, fentanyl or sufentanil on etomidate induction with respect to hemodynamics, conscious level changes and drug consumption.Methods Ninety unpremedicated and normotensive patients with American Society of Anesthesiologists (ASA) physical status I or II undergoing elective major abdominal surgery were randomly assigned in a double blinded fashion to each of the three groups: groups F, R and S. A bolus dose of fentanyl 1 μg/kg, sufentanil 0.1 μg/kg or remifentanil 1 μg/kg was given over 60 seconds in groups F, S and R, respectively. In each instance this loading dose was followed by a continuous infusion (0.1,0.01 or 0.1μg·kg~(-1)·min~(-1) of fentanyl,sufentanil or remifentanil,respectively).After 5 minutes from start of opioid infusion, etomidate was titrated at a rate of 20 mg/min to a decrease in bispectral index (BIS) to 50. The time from administration of etomidate to loss of eyelash reflex or to a decrease in BIS to 50 was recorded. The blood pressure and heart rate were also recorded at different five time points. The average maximum percent changes of systolic blood pressure (Imaximal or minimal measuring value-baselinel/baseline×100%) were calculated. Results The time and the dosage of etomidate necessary to loss consciousness were greater in group F ((70.0±15.6) seconds; (0.35±0.05) mg/kg) than in groups S ((52.3±15.9) seconds; (0.26±0.06) mg/kg) and R ((56.2±20.2) seconds; (0.27±0.07) mg/kg) (P <0.01). The three groups took similar time and amount of etomidate to achieve an adequate depth anesthesia (BIS=50). The average maximum changes of systolic blood pressure were significantly different among the three groups: F, (25±6)% vs R, (13±4)% or S, (12±5)% (P<0.001). The endotracheal intubation caused marked increases in blood pressure and heart rate in groups F and S, but not in group R, respectively (P <0.01). The great hemodynamic changes occurred more frequently in group F than in groups R and S (P <0.01). The incidence of heart rate decreases of more than 30% of the baselines after induction was higher in group R compared with groups F and S (P<0.01). Conclusions In normotensive and unpremedicated young adult patients receiving etomidate induction, low dose remifentanil or sufentanil significantly reduced the time and the amount of etomidate taken to loss unconsciousness compared with low dose fentanyl, but similar time interval and doses of etomidate were required to acquire adequate depth of anesthesia (BIS=50) for these three opioids. Remifentanil was more effective in blunting the cardiovascular responses to endotracheal intubation, nevertheless, accompanying significant lower heart rate after induction.