Concentrations of d-glucose in the blood of active and hibernating golden-mantled ground squirrels (Citellus lateralis) were determined colorimetrically using a standard (Glucostat) glucose oxidase reaction analysis. Blood from nine, fasted, active animals obtained in August averaged 183 ± 20 mg% (sd) with a range of 166–220 mg%. Blood from 25 animals that were hibernating in the established, winter pattern of hibernating behavior averaged 118 ± 20 mg% with a range of 83–153 mg%. Blood from hibernating animals was withdrawn by cardiac puncture at selected intervals including percentages (3–95% ) of the predicted hibernating periods and representative of all phases of the hibernating period. No significant changes in the level of glucose in the blood occurred throughout the hibernating period, suggesting that homeostasis of levels of glucose is characteristic throughout the hibernating period. No precipitous decrease in the level of glucose occurred towards the expected termination of the hibernating period, indicating that hypoglycemia is not the excitatory stimulus to the autonomic nervous system which elicits spontaneous arousal.