A sequence of changes in the organ of Corti associated with the destruction of outer hair cells (OHCs) and their replacement by supporting cells following chronic gentamicin treatment has been examined using thin-sections and SEM. The progression of change of OHCs was matched by concomitant expansion of adjacent supporting cells. Hair cells ruptured in the lateral membrane. The apical fragment was retained in the reticular lamina and became surrounded basally by the expanded supporting cells. No large breaches at the surface of the organ of Corti were formed. Rather, it appeared that the tight junctions around the hair cell were maintained until junctions were established between newly adjacent supporting cells in the space once occupied by the hair cell body. Only then was the OHC apex disrupted and the debris released into the sub-tectorial space. Some features of the OHC degeneration process were reminiscent of the controlled, cellular self-destruction phenomenon of apoptosis. The results suggest the possibility that the processes of hair cell loss and replacement may be controlled enabling maintenance of permeability barriers during structural reorganisation.