Responsiveness in the cochlear nucleus complex and inferior colliculus of the mouse to tonal stimulation is labelled via immunocytochemically stained Fos protein that is expressed by c-fos gene activation in excited neurons. The locations of Fos-positive neurons closely reproduce the tonotopic maps in the dorsal cochlear nucleus and inferior colliculus. Thus, the c-fos method can demonstrate stimulus-related local neuronal activation on a single-cell level and may be useful to complement other mapping techniques such as electrophysiological recording or 2-deoxyglucose autoradiography.