The technique of fluorochromasia has been used to study cellular permeability of the inner ear tissues. The hair cells of the organ of Corti show variations in permeability which are dependent on the previous history of in vivo exposure to physiologically normal levels of sound. Permeability was also sensitive to oxygen deprivation. Gross mechanical stimulation of the hair cells is sufficient to render the hair cell permeable to large molecules. The cilia of the hair cells seem to have a membrane structure independent of the hair cell itself.