The hypothalamus plays an important role in the control of food intake in different species, but there is little relevant information for ruminants like sheep. In order to study the putative role of several hypothalamic nuclei in food intake in sheep, Fos expression, a marker of cellular activity, was compared by immunohistochemistry between fed and unfed ewes. The expression of Fos protein was stimulated in the supraoptic nucleus of fed ewes, whereas it was increased in the paraventricular nucleus of unfed animals. In the latter nucleus, Fos immunoreactivity was mainly localized close to the third ventricle, an area corresponding to the parvocellular system of the nucleus, but never in the magnocellular system. In the paraventricular nucleus, the number of corticotrophin releasing factor-immunoreactive neurons and the number of Fos/corticotrophin releasing factor double-labelled neurons were not affected by feeding or lack of feeding. The number of Fos-immunoreactive neurons was higher in the lateral septum, the infundibular, the ventromedial and in the dorsomedial nuclei of unfed ewes than in those of fed ewes. Our results show for the first time that the dorsomedial and ventromedial nuclei are involved in the control of feeding in sheep as in rodents. The supraoptic nucleus of sheep is activated by the same conditions as in rodents but, conversely, the paraventricular nucleus is activated in unfed sheep, whereas in rodents and primates, this nucleus is activated by satiety as well as by fasting. In sheep, unlike in rodents, corticotrophin releasing factor did not appear to be involved in short-term regulation of food intake.