The patients who are scheduled to undergo general anesthesia are enrolled in this study. 120 patients will be randomly allocated to 3 groups(P, PR, PMR). The patients in group P will receive general anesthesia only with propofol and group PR and PMR will receive 0.25 mcg/kg/min remifentanil infusion prior to propofol. The patients in group PMR will receive 0.03 mg/kg bolus dose of midazolam 1 min after start of the remifentanil infusion. 'Success' is defined as loss of both verbal response and eyelash reflex in 2 min after propofol administration. When 'success', the next patient will receive the same dose(in 18/19 probability) or 0.25 mg/kg lower dose(in 1/19 probability) of propofol. When 'failure', the next patient will receive 0.25 mg/kg higher dose of propofol at induction period.