To study some metabolic features during feeding in food-restricted rats two groups of animals were maintained on a 2 hr feeding/22 hr fast schedule. Group D (n = 38) received a meal every day from 8:00 to 10:00 a.m. Group N (n = 34) was given the meal from 8:00 to 10:00 p.m. The average total amount of food ingested by rats of group N in the two hour period was 6.3 +/- 0.4 whereas Group D ingested 4.8 +/- 0.3 g/100 g b.w. The metabolic pattern also was different in one group as to the other. The basal liver glycogen content when feeding started was considerably lower in the nocturnal group (0.14 +/- 0.02 mg/100 mg of liver tissue) than in the diurnal group (0.44 +/- 0.10 mg/100 mg). Afterwards glycogen increased in both groups but more steeply and intensely in group N. Glycemia increased in group D and was almost invariant in group N. Insulinemia went up in both groups but in group D its peak was higher and occurred 60 minutes after the onset of feeding whereas the peak in group N was much lower and occurred at 90 minutes. There was a clear dissociation between the time courses of insulinemia and glycemia in both groups, especially in group N, which suggests a central control of insulin secretion during feeding that partially unlocks it from blood glucose concentration. The hepatic glycogen content was partially linked to the amount of food ingested but again there was a dissociation between these two variables, inasmuch as a higher glycogen replenishment in the nocturnal group corresponded to a larger food intake.