Four months after the selective ablation of inner hair cells by carboplatin, the interdental cell epithelium exhibited dilated intercellular spaces and cytosolic vacuoles not seen in controls. In addition, the wide, often electron-lucent phalanges observed in the interdental cells of the normal chinchilla collapsed into a dense stratum that projected enlarged polypoid profiles into the limbal zone of the tectorial membrane. Carboplatin treatment also resulted in the restructuring of the tectorial membrane overlying the limbus. Changes in this membrane included a variable accumulation of the basal matrix, the rearrangement of intermediate lucent spaces, and the disappearance of a superimposed filamentous mesh. These three strata are, under normal conditions, apparently involved in events underlying tectorial membrane renewal. The post-carboplatin changes in the interdental cells and tectorial membrane occurred exclusively in the proposed medial pathway for K+ diffusion from inner hair cells and presumably resulted from a reduced flow of ions and fluid secondary to the ablation of these cells.