BACKGROUND: Propofol is useful agents for anesthesia induction and maintenance, but pain on injection and possible hypotension are a commonly encountered problems during induction. Meanwhile, ketamine has potent analgesic and sympathomimetic effect. Therefore, we evaluated the effect of ketamine pretreatment on injection pain and hemodynamic changes during induction with propofol. METHODS: Premedicated one hundred and twenty ASA physical status I or II patients scheduled for elective surgery were randomly allocated into one of four groups (group 1; propofol only, group 2, 3, 4; pretreatment with 25%, 50%, 75% dose of hypnotic ED50 of ketamine, respectively) groups. Intensity and frequency of injection pain, mean arterial pressure and pulse rate were checked for evaluation of ketamine pretreatment on injection pain and hemodynamic changes during induction with propofol. RESULTS: Incidence of pain on injection was significantly reduced in group 2,3 and 4 compared with group 1. Group 2 and 3 showed more stable hemodynamic changes than Group 1 and 4. CONCLUSIONS: 25-50% of hypnotic ED50 of ketamine (0.17-0.33 mg/kg) pretreatment reduced pain on injection and hemodynamic changes during propofol induction significantly.