1. Glucose and ketone body metabolism was studied in prairie dogs, which can withstand periods of food and water deprivation at near normal body temperatures without apparent utilization of body protein. 2. Plasma glucose concentrations decreased by 18% (from 8.39 to 6.83 mM) when animals were deprived of food and water for 14 days during winter, and 27% (from 7.89 to 5.78 mM) after similar treatment in summer. 3. Glucose utilization rates decreased by 33% (from 41.0 to 27.5 mumol/min/kg) during winter food and water deprivation, but changed little in summer animals (from 26.0 to 21.1 mumol/min/kg). 4. Glucose carbon recycling was 30-31% in winter animals, but essentially zero in summer animals and did not change due to food and water deprivation. 5. Analysis of the fatty acid composition of prairie dog adipose tissue showed no evidence of odd-number carbon fatty acids, a potential source of glucose carbon. No change in adrenal weights were noted. 6. Ketone body concentrations increased 16-fold (from 0.039 to 0.641 mM) after food and water deprivation in the winter, while utilization rates increased 12-fold (from 0.42 to 4.88 mumol/min/100 g). 7. These results are discussed in relation to the ability of the prairie dog to adapt to long-term food and water deprivation.