In 24-hr water-deprived rats, naloxone, at various doses (0, 12.5, 25, 50 micrograms/rat), was administered prior to a 15-min drinking period. Infusions were made bilaterally into each lateral ventricle, frontal cortex, lateral preoptic area, lateral hypothalamus, and caudate nucleus. Naloxone reliably reduced water consumption at 50 micrograms/rat when infused into the lateral ventricles and lateral hypothalamic areas. When comparable doses of naloxone were given by peripheral injection, no effect on drinking was observed. There appeared to be a trend developing for greater sensitivity to naloxone when infusions were made into a particular part of the hypothalamus. These data support the idea that naloxone reduces drinking by acting at central opiate receptors.