The effect of injection of norepinephrine in the anterior regions of hypothalamus on rectal temperature, skin temperature, heart rate and respiratory rate in rhesus monkeys was studied. The injection of 2 micrograms of norepinephrine in the preoptic area produced a fall in body temperature without any accompanying change in skin temperature, heart rate and respiratory rate. The findings suggest that the suppression of heat production may be responsible for the norepinephrine induced hypothermia in monkeys.