1. With use of a liquid-conditioned coverall, the thermoregulatory responses to a lowering of environmental temperature from 35°C to 23°C were assessed in eight normally nourished and six undernourished elderly female patients, during their convalescence after surgical repair of a fracture of the femoral neck.
2. There was no difference in the peripheral vasoconstriction of the two groups in response to a cold environment.
3. On lowering the environmental temperature, the increase in metabolic rate was significantly impaired in the undernourished group compared with the normally nourished group (P < 0.05).
4. There was a small decrease in core temperature in the undernourished group (median change −0.1°C) during the period of exposure to the lowest environmental temperature (23°C). This was significantly different from the lack of change (median change 0°C) in core temperature observed in the normally nourished group (P < 0.05).
5. This defect of thermogenesis may underlie the propensity of undernourished elderly patients to suffer hypothermia and fracture of the femoral neck in the winter months.