<正> Forty rots were randomized into 2 groups and naloxone or saline were injected to therats after they were inflicted with hemorrhagic shock at sea level and at a simulated altitude of4000m respectively to observe the effects of naloxone on left ventricular systolic pressure（LVSP）

left ventricular diastolic pressure（LVDP）

the maximal changing rate of LVSP（dp/dt max）

heartrate（HR）

and survival time of the animals.Plasma β-endorphin（β-EP）was determined beforeand after hemorrhage to observe the relationship between β-EP and hemorrhagic shock.It wasfound that the circulatory parameters of hemorrhagic shock changed more markedly at high alti-tude than at sea level

naloxone could restore these parameters and prolong the survival time inboth the animals of the sea level and high altitude groups

and plasma β-EP level was elevatedafter hemorrhage especially in those animals at high altitude.These findings indicate:（1）Hemorrhagic shock at high altitude is usually accompanied with severe clinical manifestations

rapid progression

and high mortality.（2）β-EP seems to participate in the pathologicalmanifestafions of hemorrhagic shock at high altitude

and its depressive action on myocardialcontraction may be one of the factors inducing hemorrhagic shock.（3）Naloxone possesses defi-nite property to comet hemorrhagic shock at high altitude.