Abstract: The concentrations of endothelin were measured by radioimmunoassay in 15 rats after being placed in low atmospheric pressure (36.971 kPa) hypoxia for 30 min to mimic the flying altitude of 7500 m. Compared with the control, the concentration of plasma endothelin of the experimental group increased markedly (P＜0.001)> and the concentrations of endothelin in lung, right atrial myocardium and thalamus decreased significantly (P＜0.001). The results suggest that the synthesis, release and metabolism of the endothelin in the experimental subjects developed serious disturbance by acute hypoxia, which may be significant in the damages of the body in hypoxia.