BACKGROUND: Propofol is increasingly being used as an anesthetic since the introduction of the TCI (target controlled infusion) technique, but previous reports have demonstrated that hypotension and injection pain occur especially during fast infusion of propofol. We therefore studied the effect of ketamine preadministration on induction and recovery when using propofol TCI. METHODS: Thirty-four patients undergoing elective surgery within 2 hours were randomly assigned to one of two groups according to induction methods; Group P (propofol TCI, 6 microgram/ml, flash mode), Group KP (ketamine 0.25 mg/kg followed by propofol TCI, 4.5 microgram/ml, flash mode). Anesthesia was maintained with fentanyl, N2O, and propofol TCI. Outcome measures were induction time, injection pain, hemodynamic responses during induction period, propofol doses, emergence time and postoperative side effects. RESULTS: Incidence of injection pain and induction dose of propofol were significantly reduced in Group KP but there was no significant difference in induction time, emergence time or postoperative side effects between two groups. Heart rates showed no differences between the two groups, but the changes of mean arterial pressures from base line at 30 sec after intubation were significantly greater in Group P compared to Group KP. CONCLUSIONS: During fast induction with the flash mode of propofol TCI, small amounts of ketamine preadministration could significantly reduce the target concentration for hypnosis, injection pain and hemodynamic changes without a delay of emergence and an increase of postoperative side effects.