The avian inner ear possesses a remarkable capacity for the regeneration of sensory receptors after acoustic trauma or ototoxicity. Most replacement hair cells are created by renewed cell division within the sensory epithelium, although some new hair cells may also arise through nonmitotic mechanisms. Current data indicate that epithelial supporting cells play an essential role in regeneration, by serving as progenitor cells. In order to become progenitors, however, supporting cells may need to undergo partial dedifferentiation. In this review, I describe molecules that are expressed by supporting cells in the avian ear. Although a number of these molecules are likely to be critical to the maintenance of the supporting cell phenotype, we presently know very little about phenotypic changes in supporting cells during the early phase of regeneration.