The localization of three glutathione S-transferase (GST) isoforms in the rat cochlea was examined using specific antibodies against each isoform. GST immunoreactivities were found in particular parts of the cochlea, including the intermediate cells and the basal cells of the stria vascularis and various types of fibrocytes in the spiral ligament. The different cell types showed varying combinations of GST isoforms. The GST immunopositive cells identified in the present study may play a central role in the metabolism and inactivation of endogenous and exogenous ototoxic compounds. The specific arrangements also indicated a possible contribution to the detoxification process in the form of a blood-labyrinth barrier.