BACKGROUND: The Pharmacokinetic parameter and the degree of dilution can have an effect on induction time and vital signs during general anesthesia with propofol. Induction time, induction dose and vital signs according to various flow rates and the degrees of dilution during anesthesia induction with propofol were studied. METHODS: After institutional review board approval, and informed consent, One hundred and eighty ASA I or II adult patients undergoing elective surgery were assigned to one of four groups according to their degree of dilution. One group was undiluted and another 3 groups were diluted with 5% D/W (1:1, 1:2, 1:3). Each group was divided into 3 subgroups according to their flow rates of 25, 50, 100 mg/kg/hr. No premedication was given. With routine monitoring including radial arterial cannulation, propofol was infused using a syringe or infusion pump (Becton Dickinson pump, Franklin Lakes New Jersey, USA) in the previously designed manner. Induction time defined as loss of eyelash reflex, induction dose, and vital signs were checked. RESULTS: The faster the flow rate and the more diluted a drug, the shorter the induction time. The faster the flow rate and the less diluted a drug, the greater the induction dose. The more diluted a drug, the less the decrease in systolic blood pressure. Flow rate has little influenced decreasing systolic blood pressure. CONCLUSIONS: We concluded that it is reasonable to reduce flow rate and dilute propofol when the hemodynamic changes of the patient should be minimal during propofol based sedation/anesthesia.