Freeze fracture has been used to examine junctional complexes within the gentamicin damaged guinea pig organ of Corti during the period of structural reorganisation associated with hair cell loss. When examined up to 28 days after a regime of chronic gentamicin administration, no significant alterations to the pattern or nature of the complex tight junctions associated with the hair cell apex could be detected. In contrast, marked abnormalities of the junctions between adjacent supporting cells, and evidence of formation of new gap junctions on the lateral membranes of Deiter's cell was seen. The use of lanthanum as an electron dense tracer in thin sections also showed that no breakdown of permeability barriers occurred in the reticular lamina. These results support the concept of a controlled response by the organ of Corti, with conservation of the tight junction of the hair cell and maintenance of permeability barriers. Early changes to the membranes of the stereocilia and lateral cisternae of the outer hair cells were also identified. These may indicate direct effects of gentamicin upon membrane structure.