BACKGROUND: Propofol has been found to be an ideal anesthetic for sedation during regional anesthesia with the advantage of rapid onset of action and recovery. Infusion of propofol by target-controlled infusion (TCI) has been shown to be effective in achieving conscious sedation. The purpose of this study was to define the optimal target concentration of propofol evaluated by bispectral index (BIS) which is necessary for conscious sedation in patients to achieve a local or regional blockade. METHODS: Sixty patients scheduled to undergo local or regional anesthesia were divided into 3 groups. 10 20 min after performing local anesthesia with 2% lidocaine 10 ml (group 1), spinal anesthesia with 0.5% hyperbaric bupivacaine 12 18 mg (group 2) or brachial plexus block with 1% lidocaine 40 ml (group 3), TCI of propofol was started at a target plasma level of 1 microgram/ml and the target concentration was adjusted in steps of 0.2 microgram/ml to maintain a sedation level comparable to an Observer's Assessment of Alertness/Sedation (OAA/S) score of 3. BIS, EKG, heart rate, noninvasive arterial blood pressure, respiratory rate and SpO2 were recorded during the operation. RESULTS: Group 1 had a significantly higher mean (range) target concentration [1.8 (0.9 2.8) microgram/ml] than group 2 [0.9 (0.2 2.4) microgram/ml] and group 3 [1.0 (0.2 2.6) microgram/ml]. A target concentration of 0.9 1.8 microgram/ml of propofol produced BIS 78.2 (group 1), 73.4 (group 2) and 75.4 (group 3). CONCLUSIONS: TCI of propofol with a 0.9 1.8 microgram/ml blood concentration produces safe sedation during locoregional anesthesia without severe complications.