Electronmicroscopic immunogold cytochemistry was applied to investigate the localization of glutathione (GSH) in the guinea pig inner ear. GSH immunoreactivity was preferentially distributed in basal cells and intermediate cells of the stria vascularis, and in fibrocytes and capillary endothelial cells in the spiral ligament and vestibular endorgans. The present findings suggest that the synthesis of GSH, a peptide known to protect against ototoxic compounds, depends on restricted cell populations in the inner ear.