The opiate antagonist naloxone has been used to treat shock following acute blood loss in conscious rats. Naloxone treatment rapidly increased mean arterial pressure and pulse pressure in this new shock model. More importantly, these blood pressure changes were sustained and survival was significantly increased with maloxone as compared with placebo treatment. From these findings, it may be inferred that endorphins may play a role in the pathophysiology of hypovolemic shock. It is suggested that narcotic antagonists may prove to be of therapeutic value in the treatment of shock.