Using a double immunostaining technique with unconjugated cholera toxin (CT) as a retrograde tracer, we have demonstrated in the cat that the nucleus raphe pallidus receives two major afferent projections from the hypothalamus: the preoptic periventricular nucleus; and the peri- and paraventricular zones of the posterior hypothalamic area. Some CT-labeled neurons in the preoptic periventricular nucleus showed Met-Enk-like immunoreactivity, while many CT-labeled neurons in the posterior hypothalamic area presented either corticotropin-releasing-factor-like or Met-Enk-like immunoreactivity.