The influence of afferent input on the survival of target neurons in mammals has been examined by the removal of one eye of pouch young of the marsupial native cat (Dasyurus hallucatus). The ages at eye removal spanned the period of neurogenesis of the ascending visual pathway, and were earlier than the time of maximal axon number in the optic nerve. Autoradiography following the injection of tritiated proline into the intact eye of adult animals shows that the lateral geniculate nucleus contralateral to the injected eye of the earliest enucleates retains its laminated structure, despite the total absence of binocular competition throughout development. However, we find a dramatic, age-related reduction in the volume of those parts of the lateral geniculate nucleus and superior colliculus which would normally receive a contralateral-only projection from the enucleated eye. The effects of the enucleation are not restricted to the primary termination sites of the optic axons but ramify throughout a large part of the neo- and archicortex.