Naloxone (0.5--5 mg/kg) reduced both food and water intake in non-deprived male rats, tested in the dark phase of the light-dark cycles in their home cages. These effects were transient; food and water-intake were restored to control levels by the end of the 8-h test period. The effects were also not dose-related. Naloxone (1 and 5 mg/kg) also reduced water-intake in water-deprived and food-deprived animals, without altering food-intake. These results suggested that naloxone may exert a primary antidipsogenic action, that does not depend upon any suppression of feeding. A final experiment showed that naloxone can completely abolish the thirst produced by injection of a hypertonic saline solution. This experiment also demonstrated that naloxone could suppress feeding, even though food intake was markedly inhibited by the osmotic thirst stimulus. Hence, the activation of feeding responses (e.g. by food deprivation) is not a necessary condition for naloxone to suppress feeding. The implications of these results for the control of feeding and drinking responses are briefly considered.