Epidural and subarachnoid narcotics have raised new possibilities for selective blockade of pain transmission at the spinal cord level. However, it must still be regarded as an experimental technique until detailed pharmacological and physiological data are available, since many reports have treated the development of respiratory arrest which may be related to the dynamics fo CSF flow. We experienced 2 cases of respiratory arrest after intrathecal injection of 2mg morphine. One patient developed respiratory arrest at approximately 5 1/2 hours after intrathecal morphine and the other at approximately 12 1/2 hours. Those respiratory arrests were completely reversed with naloxone hydrochloride without interfering with the analgesic effect of the drug.