Thermoregulatory mechanisms are influenced by the temperature of the postnatal environment. Animals reared in cool environments are more tolerant of cold as adults, whereas those reared in warm conditions are more tolerant of heat. Because diet-induced and thermoregulatory thermogenesis share common features, studies examined the impact of rearing temperature on weight gain and fat accumulation. Rats reared at 18 degrees C gained more weight and accumulated more fat in abdominal depots than animals reared at 30 degrees C when both were housed at a common temperature, responses that were exacerbated by ad libitum access to sucrose. Male rats reared at 30 degrees C were less affected by sucrose than 18 degrees C-reared males, whereas female rats reared at 18 or 30 degrees C were similarly susceptible. During exposure to 18 degrees C, fat accumulation in abdominal depots increased in males but decreased in females. These data suggest that early temperature exposure influences weight gain and fat accumulation in later life, a difference that is most apparent when animals are housed at a common temperature.