1. 1.|Hypothalamic and rectal temperatures were recorded in 8 warm-reared (wr) and in 12 warm-acclimated control rats during resting in the heat and during 30 min running under thermoneutral conditions.
2. 2.|Brain and body temperatures of wr rats were significantly higher (P < 0.001) than control rats, both in normothermia as well as in hyperthermia; at rest, and also during exercise.
3. 3.|Warm-reared rats were more tolerant to heat.
4. 4.|During normothermia a weak selective brain cooling was present in control but absent in wr rats. During hyperthermia, however, the cooling intensified in control and occurred in wr rats.
5. 5.|The main strategy of adaptation to heat in wr rats is an upward resetting of the temperature set-point and increased passivity.