The possible beneficial actions of naloxone (NAL) were evaluated in canine splanchnic arterial occlusion (SAO). MEan arterial pressure (MAP), cardiac output (CO) and left ventricular contractility (LV dP/dt max) were measured in pentobarbital anesthetized dogs. Animals received intravenously NAL (8 mg/kg) or an equivalent volume of 0.9% saline prior to occlusion or sham occlusion, followed by infusion of 8 mg/kg/hr. The occlusion was released after 2 hr and the dogs monitored for an additional 3 hr or until MAP fell to 40 mmHg. Blood was drawn during the experiments for analysis of dopamine (DA), norepinephrine (NE) and epinephrine (E). SAO and SAO + NAL dogs had decreased MAP and CO after release. However, SAO + NAL animals had a higher LV dP/dt max. NAL in sham and SAO dogs produced significantly higher plasma DA and E levels than in their respective control groups. 67% of SAO + NAL survived 3 hr post release, compared to 43% of SAO dogs. Although the mechanism of NAL protection remains undefined, it may relate to altered vascular response to endogenous opiates or catecholamines.