Orange fluorescent granules are numerous in the acoustic nerve in the rat and the mouse. The granules are often accumulated in masses distributed along, or within, the acoustic nerve neurons within the cochlear modiolus. They are not found more peripheralward. The orange fluorescing granules are not autofluorescent; they are absent in sections mounted directly from the cryostat, and the fluorescence disappears in sections treated with water or dilute isopropanol. The fluorescence is sensitive to ultraviolet light and largely disappears after treatment with α-methyl- m-tyrosine or reserpine (24 hr). Heat alone induces some orange fluorescence, restricted to the distal ends of the axons of the neurons. Spectrofluorometric analyses of heat-induced and vapor-induced orange fluorescence have thus far failed to demonstrate significant spectral differences. It is concluded that orange fluorescence may indicate the presence of an amine in a distinctive storage form.