A decrease in the oxygen supply to the inner ear by reduced cerebrovascular circulation results in a decrease in the endocochlear potential, the cochlear microphonics, and the action potential of the acoustic nerve. To evaluate the effect of acute systemic blood loss on the auditory pathway, the change of auditory brain stem response was observed in rabbits after experimental blood loss. 1) After acute blood loss, the wave V latency was slowly prolonged and the maximal prolongation was observed in 150 minutes and it was continued until 330 minutes following acute blood loss. 2) After 150 Minutes following acute blood loss, a group with autotransfused, showed recovery of wave V latency and returned to normal in 330 minutes. 3) In a group with infusion of low molecular dextran during acute blood loss, the change of wave V latency was not observed. These results suggest that the acute systemic blood loss causes the change of ABR pattern and it may be due to hypovolemia.