Oxygen consumption and CO2 production were measured on four female snowy owls at several different ambient temperatures and two air speeds. Food consumption and existence metabolism were measured on individuals caged indoors at three ambient temperatures and on individuals caged outdoors in winter at Barrow, Alaska. Standard metabolism is 42% less than the value computed with the equation of Lasiewski and Dawson (1967). The thermoneutral zone extends from 2.5 through 18.5°C. Thermal conductance of the snowy owl (0.05 cal · g-1 · hr-1 · °C-1) is lower than any published for an avian species and is equivalent to that of the pelts of the arctic fox and Dall sheep. Oxygen consumption of owls exposed to air speeds of 4.47 m sec-1 and 7.47 m sec-1 increases approximately with the square root of air speed. Lower critical temperature in a 7.47 m sec-1 wind appears to increase at least 11°C above that at negligible air speed. Existence metabolism at 5°C, -4.5°C and -17.8°C was, respectively, 2.15, 1.73, and 1.4 times greater than standard metabolism. At ambient temperatures (TA) below -4.5°C existence metabolism (EM.) is expressed in kcal day-1 by the equation, E.M. = 191.68 -5.69 TA. Efficiency of energy utilization A (100 · metabolized energy gross energy intake-1) for owls indoors was 70%, for owls outdoors, 74 to 80%. Computed minimal daily food consumption for a free-living owl residing near Barrow, Alaska, in the fall and winter of 1966–67 ranged from 4 to 6.7 sixty-gram lemmings. Food consumption and metabolized energy of owls caged outdoors at Barrow, Alaska, were compared with values measured indoors. Food consumption of caged owls was compared with published field observations of food consumption.