OBJECTIVE Although ropivacaine has been extensively studied for epidural anesthesia, very few reports exist on brachial plexus block. We therefore decided to investigate the clinical features of axillary brachial plexus anesthesia with two different concentrations of ropivacaine (0.5% and 0.75%) and to compare the results with those obtained with 0.5% bupivacaine. METHODS Three groups of patients were randomized and prospectively studied. They received, in a double-blind fashion, 32 mL of the local anesthetic solution into the midaxilla, by a nerve-stimulator technique. Onset time in each of the stimulated nerves was recorded both for the sensory and motor block. Peak time (ready to surgery), rate of supplemental blocks, need for intraoperative opioids, duration of sensory and motor block, postoperative analgesic requirements, and patient satisfaction were also recorded. RESULTS The rate of complete sensory and motor block observed with both ropivacaine groups was higher at 10, 15, and 20 minutes postinjection (P < .001). The mean peak time was shorter with ropivacaine than with bupivacaine (R50 = 16.37 minutes, R75 = 14.7 minutes, B = 22.3 minutes, P < .05). The quality of the anesthesia was higher with ropivacaine, as measured by the intraoperative needs for opioids and the overall patient's satisfaction (P < .05). No significant differences were noted with all the other studied parameters. CONCLUSIONS Ropivacaine showed advantages over bupivacaine for axillary brachial plexus block. Because no statistical differences were found between the two ropivacaine groups, we therefore conclude that 0.75% does not add benefit and that 0.5% ropivacaine should be used to perform axillary brachial plexus blocks.