Small thermocouple sensors were surgically implanted in the liver, kidney, hind leg muscle, interscapular brown adipose tissue, small and large intestines, dorso-lumbar internal side of the skin, periovaric adipose tissue and the lower aorta of Wistar rats. The aortic temperature was taken as core temperature. The sensors allowed continuous long-term monitoring of the temperatures of these organs. A period of 18 hours of food deprivation resulted in an overall decrease of mean core and organ temperature, brown adipose tissue temperature dropping to values lower than those of the aorta in the fed state. Liver, kidney and small intestine maintained higher temperatures than the aorta both in fed and starved states. Refeeding overshot the core temperature with increases in most organs versus both the fed and food-deprived situations. The results are concordant with an active role of brown adipose tissue in dietary induced thermogenesis. Three days of food deprivation did not alter the basic circadian rhythm of core temperatures in the rat kept at 22 degrees C, whereas it did modulate both nightly maximum and diurnal minimum temperatures to much lower settings than either in the fed or refed situations. The rat adapts to starvation by decreasing core and organ temperatures and widening the amplitude of the daily temperature cycle.