1. The effects of acute alterations in energy intake on the thermoregulatory responses to a cooling stimulus were studied in healthy, normal weight, young female subjects. On separate occasions, seven subjects were underfed for 7 days at 60 kJ day-1 kg-1 ideal body weight and six subjects were starved for 48 h. The cooling stimulus was provided by a coverall perfused with water at 16 degrees C. 2. After the application of the cooling stimulus, central body (auditory canal) temperature rose initially in both studies. After underfeeding, the magnitude of this rise in temperature was not significantly different from that seen in the normally fed state. After 48 h starvation, the rise in temperature on cooling was reduced from 0.30 (SEM 0.03) to 0.10 (0.04) degrees C (P less than 0.01). In two subjects in whom central body temperature had been maintained in the normally fed state, a fall occurred after starvation. 3. Underfeeding for 7 days did not affect thermogenesis or the degree of vasoconstriction in the forearm or hand in response to cooling. 4. After 48 h starvation, the thermogenic response to cooling was abolished and blood flow in the forearm remained higher than in the normally fed state. 5. In normal weight young females, thermoregulatory responses to a cooling stimulus were therefore substantially affected by 48 h starvation but not by 7 days underfeeding.