Endothelin (ET) has been revealed to be a local hormonal regulator of pressure, fluid, ions and neurotransmitters. In order to investigate the mechanism of homeostasis within the microenvironment of the inner ear, the present study has examined the distribution of ET in the vestibule of normal guinea pigs, by immunohistochemistry using mouse antihuman ET IgGl monoclonal antibody. ET-like activity was identified in the sensory epithelial cells, supporting cells, dark cells, transitional cells, vestibular membrane, semicircular wall cells and vestibular ganglion cells. These findings suggest that ET may play an important role in maintaining homeostasis of the vestibule.