Plasma glucose, free fatty acids, and triglycerides were measured in captive ruffed grouse (Bonasa umbellus) acclimatized to deep winter conditions, and in controls held at 22 °C. Levels of these metabolites indicated a significant hyperglycemia in the winter-acclimatized grouse, but no lipolytic response was observed. The glycogen content of the liver and pectoral muscles of grouse acclimated to −10 °C for 4 weeks was significantly higher than the control levels. The percentage ether-extractable lipid content of wild grouse collected from January to August was low (5.91–9.17% of dry weight) and showed no significant changes during these months. The pectoral muscles and liver made up 31.8–36.6% and 1.14–1.64% of the total body weight, respectively, but marked changes in the proportions of these tissues did not occur from January to August.Ruffed grouse contain very small energy reserves. The respective roles of carbohydrates and fats in thermogenesis are discussed, as well as estimates of the energy available from fat and glycogen reserves compared with the daily energy requirements of grouse. The importance of regular feeding, together with behavioral and plumage adaptations which restrict heat loss, is emphasized in the maintenance of an energy balance during winter conditions.