Changes in the surface morphology of the organ of Corti in the chinchilla were studied following exposure to blast waves at 160 dB peak SPL. The generation and development of a mechanically induced lesion on the organ of Corti was followed over a period of 30 days using scanning electron microscopy. The most prominent feature of the lesion was the complete separation of a 5-7 mm strip of the sensory epithelia consisting of outer hair cells, Deiter cells and Hensen cells from the reticular lamina and the basilar membrane. The inner hair cells in this same area survived for several days in a remarkably normal condition. A spectrum of ciliary changes was observed on the inner and outer hair cells that differ somewhat from those commonly reported following continuous noise exposure. Some of the observed changes in morphology can be related to a variety of inferred mechanical events on the basilar membrane.