This work was performed to investigate the effect of duration of fasting in the responses of chickens peripherally injected with histamine on the regulation of food intake. The animals were 16-week-old male chickens from layer-strain and the doses of histamine used were 500 and 1000 microg/kg of body weight. The non fasted chickens showed no effect of histamine on the food intake. When the animals were fasted during 4 h, injected with the histamine and immediately refed, the results showed a reduction of food intake only the first 15 min of the experiments with the dose of 1000 mug. In chickens fasted during 16 h or 26 h and refed, the histamine inhibited significantly the food intake at all time with the two doses. When the animals were fasted 16 h and refed during 60 min before the administration of the histamine, there is no inhibition of food intake. No effect on water intake has been registered in all the experiments. The blockade of the action of histamine injected in chickens fasted during 16 h by cimetidine and promethazine, show that the inhibition of food intake occurs through the H1 but not through H2 receptors. The fasting used in paradigm to investigate the effect of drugs such as histamine on the appetite, can affect differently the responses according to its duration, as observed here in chickens.