The spiral ganglia of the cat, gerbil, mouse, rat, and human were immunohistochemically stained with various monoclonal neurofilament antibodies. Three antibodies to the 200-kD neurofilament protein (R-3, Dräger et al.,'84; ICN anti-200, clone NE14, Debus et al.,'83; RT-97, Wood and Anderton,'81) labeled the somata of type II spiral ganglion neurons but not those of type I ganglion neurons. In the extreme base of the cochlea of cats, mice and rats, there was intense labeling of a few (< 0.5% of the total ganglion population) large neurons resembling type I ganglion neurons.