Food intake is the homoeostatic behaviour through which all beings regulate their energy balance. Short-term control is exerted by the brain at each meal, according to the nutritional requirements. The purpose of this control is to ensure long-term regulation of the energy (or adipose) mass reserve which is the principal determinant of bodyweight. After 75 years of investigation, it now appears that the systemic stimulus which initiates food intake probably is a fall in the capacity of cells to produce energy (and therefore power) and that this parameter is most likely to be measured by hypothalamic receptors. The discontinuation of food ingestion behaviour always takes long before the nutriments ingested have been absorbed and have been able to correct the hunger signal. This means that it has its own inhibitory mechanisms the starting point of which is the various sensitivities aroused by food intake and by nutriments before they reach the milieu interne, viz.: the oronaso-pharyngeal analyser system, the gastric stretch receptors and the intestinal or portal-hepatic chemoreceptors. Their activation rests on conditioning processes or on reflex processes one of the effects of which is to induce a change in the affective component associated with food stimuli. It is through these mechanisms that hedonic factors are integrated in the control of food intake. In terms of neurophysiology, it is certain that the main role is played by the ventro-medial and lateral nuclei of the thalamus, although these nuclei should no longer be regarded as centres of hunger or satiety but as integrating areas acting synergistically with many other cerebral structures.(ABSTRACT TRUNCATED AT 250 WORDS)