BACKGROUND: In addition to its general anesthetic effect, ketamine has a local anesthetic-like action by a peripheral mechanism. We evaluated the effects of injecting ketamine 45 mg in a supraclavicular brachial plexus blockade (SBPB) with 0.5% ropivacaine 150 mg. In addition, we evaluated the incidence of side effects. METHODS: Thirty four adult patients scheduled for upper extremity surgery were randomly allocated to one of three groups; group 1 (placebo group, n = 10) received 0.5% ropivacaine 30 ml for SBPB and intravenous saline 0.9 ml, group 2 (ketamine group, n = 13) received 0.5% ropivacaine 30 ml with ketamine 0.9 ml (45 mg) for SBPB, and group 3 (control group, n = 8) received 0.5% ropivacaine 30 ml for SBPB and intravenous ketamine 0.9 ml (45 mg). At 1-minute intervals after SBPB, patients were assessed for loss of shoulder abduction, elbow flexion, and wrist flexion, and for loss of pinprick sensation in the deltoid, radial, median, and ulnar dermatomes. Side effects and sedation scores were recorded at 5-minute intervals after SBPB. Before discharge, patients were asked when full sensation or motor function recovered. RESULTS: The speeds of onset for both the motor and sensory blocks were similar in all three groups. The duration of postoperative analgesia and paralysis were similar in the three groups. Side effects were experienced by 62% of patients in group 2 and by 100% of patients in group 3. CONCLUSIONS: We found that the addition of ketamine (45 mg) to brachial plexus blockade does not offer either a quicker onset or a longer duration of anesthesia when using 0.5% ropivacaine SBPB, and it caused a relatively high incidence of side effects.