Descending projections from the lateral hypothalamic area to the brainstem were studied, using [3H]-amino acid autoradiography, in the rat. Two main ipsilateral paths were reorganized. One is the periventricular fiber system projecting to the midbrain central gray. The other is a fiber system which eventually descends the central tegmental field, projecting strongly to the dorsal raphe nucleus, medial and lateral parabrachial nuclei, nucleus reticularis parvocellularis, solitary nuclei and dorsal motor nucleus of the vagus nerve. Sparse projections were observed to the nuclei raphe magnus, obscurus and pallidus, group B3 (or the ventrolateral subpial group) and spinal trigeminal nucleus.