The quantitative analysis of fluorescence in frozen sections of rat inner ears exposed to Texas Red conjugated gentamicin revealed distinct gradients of gentamicin fluorescence. At 500 µg/ml gentamicin fluorescence occurred in inner and outer hair cells, the interdental cell region, the spiral limbus below the interdental cells, the nerve fiber bundle in the spiral lamina, the inner sulcus cells and the dorsal region of the spiral ligament. No gentamicin fluorescence was observed in the Hensen / Claudius cells, the ventral region of the spiral ligament, the stria vascularis and the spiral ganglion. In the vestibule only the hair cell epithelium and the transitional cells of the saccule showed gentamicin fluorescence while no gentamicin fluorescence was found in hair cell epithelia and transitional cells of utricle and ampule, nerve fibers below hair cell epithelia of saccule, utricle and ampule and in dark cells. The gentamicin flurescence increased at higher concentrations. Gentamicin exposure led to more pronounced gentamicin fluorescence in the cochlea compared to the vestibule. Based on the predominant gentamicin fluorescence in the hair cell - limbus region of the cochlea at a low dose we propose that gentamicin may interact with the K(+)-flow from the inner hair cells back to the scala media.