It is generally accepted that certain kinds of vertigo and hearing disturbances are caused by blood flow insufficiency in the vertebrobasilar arterial system. Using the microsphere method we investigated whether unilateral vertebral artery or unilateral posterior inferior cerebellar artery occlusion could cause an imbalance between right and left inner ear blood flow in rats. We also studied the differential vulnerability between blood flow in the cochlea and in the ampullae of the three semicircular canals. We counted the numbers of microspheres distributed to the cochlea (CO) and microspheres distributed to three ampullae of semicircular canals (SC) under a microscope with the surface preparation method. The results were as follows: i) no imbalances were observed between bilateral CO or SC even in animals with arterial occlusion, and ii) the CO/SCs of animals with arterial occlusion were not significantly different from that of the control animals. These findings suggest that total inner ear blood flow over a certain period of time was even between the ears bilaterally even in animals with arterial occlusion. The blood flow in the ampullae of the three semicircular canals was not more or less affected by arterial occlusion than the blood flow in the cochlea.