Morphine administered via the intrathecal or epidural route can produce long-lasting analgesic effect for acute and chronic pain. Unfortunately, little was known about the action of opioid drugs on the peripheral nerve system. The author administered morphine and local anesthetic when performing brachial plexus block in 64 selected cases and observed the effects of morphine on postoperative pain relief and the duration time of the local anesthetic. The following results were obtained. 1) Morphine 10mg administered in the brachial plexus block produced no significant increase in the duration of the block and no significant effect on postoperative pain relief. 2) Morphine 10mg administered in the brachial plexus block produced systemic side effects.