The effect of d-amphetamine-induced hypothermia among rats maintained at a cold ambient temperature is related to its ability to release dopamine in the dopaminergic neurons in the mesolimbic pathway. However, the physiological mechanisms which mediate the hypothermia (heat loss or a decrease in heat production) are not known. Since we have failed to demonstrate effects induced by d-amphetamine on food intake or on heat sensors on the rat's tail we conclude that these are not the mechanisms involved in hypothermia. Effects of d-amphetamine on O2 consumption and CO2 production of rats kept at various ambient temperatures were investigated in order to find out if there is any relation between a decrease in body temperature and a decrease in the Basal Metabolic Rate. Neither such relations nor any relations between levels of body temperatures and levels of motor activity were found. The problem of the peripheral mechanisms involved in d-amphetamine-induced hypothermia remain as yet unidentified.