Endogenous opiate peptides are released in early hemorrhagic shock and may mediate hypotension during hypovolemia. We compared the effects of naloxone alone versus incomplete volume resuscitation on survival and splanchnic blood flow. Dogs were bled to a MAP of 35 mm Hg for 2 hours. In eight dogs, shed blood was returned; eight dogs received naloxone (2 mg/kg bolus and 2 mg/kg/hr in 0.5 ml/kg/hr normal saline) with no shed blood returned. Seven dogs received normal saline alone without shed blood or naloxone and served as untreated controls. Untreated dogs survived a mean of 18.6 minutes. All other dogs survived for 180 minutes. Naloxone and shed blood were equally effective in improving hepatic and renal blood flow; gastric, intestinal, pancreatic, and splenic blood flow remained unchanged from shock values in both groups. These data indicate that in the face of hypovolemia naloxone improves survival and blood flow (ml/min/gm) to splanchnic organs despite no return of shed blood.