Injections of HRP into the lateral central and paracentral nuclei led to labeling of cells in various diencephalic structures of the injected side, particularly in the medial pulvinar, intralaminar, thalamic reticular and ventral lateral geniculate nuclei. A few cells were labeled in the zona incerta, field of Forel and some hypothalamic nuclei. Labeling of cells in the more caudal brain stem structures was found bilaterally, mostly with ipsilateral predominance. Some labeled cells were detected in the pretectal nuclei, periaductal gray and substantia nigra, pars reticulata. Numerous cells were labeled in the superior colliculus, mainly in layers 3 and 4. A number of labeled cells were distributed in almost the entire extent of the brain stem reticular formation. Very few labeled cells were encountered in the ipsilateral dorsal tegmental and parabranchial nuclei. A few cells were labeled in the vestibular nuclei and nucleus prepositus hypoglossi bilaterally. Some labeled cells were detected in three cerebellar nuclei on both sides. Injections of HRP into the medial central nucleus showed a different pattern of labeling. It is noteworthy that no labeled cells were seen in the dorsal thalamus, hypothalamus (except for the mamillary nucleus), superior colliculus or cerebellar nuclei.