The effects of 2 days of water deprivation on local rates of methionine incorporation into protein in 54 brain and 5 circumventricular structures of conscious freely moving rats have been examined by means of a recently developed quantitative autoradiographic method with L-[35S]-methionine. The results show that 2 days of water deprivation does not affect methionine metabolism in the majority of the brain areas analyzed, but reveals selective increases in the hypothalamoneurohypophyseal system, in cerebral structures surrounding the third ventricle, in the locus ceruleus, raphe dorsalis, nucleus ambiguus and hippocampal CA3 layer. In contrast, decreases were observed in the central amygdala, lateral habenula and interpeduncular nucleus. Although the highest increases were located in brain areas involved in body fluid homeostasis, several aspecific responses, perhaps due to chronic stress, were also observed, notably in the locus ceruleus, raphe dorsalis and in a restricted number of limbic system structures.