Resting metabolic rate (RMR) and total daily energy expenditure (TDEE) were measured on a sample of 47 adults (35 males, 12 females) from two indigenous Siberian populations, the Evenki and Keto. The Douglas bag method of indirect calorimetry was used to measure the energy cost of lying, sitting, standing, and three exercise levels of the Canadian aerobic test of fitness (step test). The flex-heart rate method of heart rate monitoring (flex-HR; Spurr et al. , Am. J. Clin. Nutr. 48:552?559) was utilized to predict TDEE from the measured energy costs. Measured RMR was 6.66 kJ/min (1.59 kcal/min) for males and 5.19 kJ/min (1.24 kcal/min) for the females. Subjects living in the bush in brigade work parties had significantly higher RMRs than those residing in the villages. Comparison of RMR to selected populations suggests that the elevated metabolism of the subjects living in the brigades is due to short-term environmental acclimatization to the ambient conditions of the taiga rather than long-term adaptation to living in a northern climate. TDEE was estimated at 11.8 ± 3.0 MJ (2,815 kcal) for men and 8.6 ± 1.9 MJ (2,056 kcal) for women, and there were no brigade-town differences in DEE. Based on their physical activity level (PAL = TDEE: basal metabolic rate [TDEE:BMR]), which was 1.77 for males and 1.59 for females, the Evenki and Keto have ?moderately? active lifestyles during the summer according to FAO/WHO/UNU guidelines (FAO/WHO/UNU  WHO Technical Support Series No. 724).