Energy expenditure during different activities of 11 laboratory workers was determined by measurement of oxygen consumption. The energy cost of various activities expressed as Calories per m2 body surface per hour were as follows: BMR 30.87 ± 0.741; lying rest 34.79 ± 0.578; sitting rest 36.61 ± 2.927; standing rest 41.24 ± 1.323; sitting study 42.85 ± 1.034; sitting work 46.79 ± 3.036; standing laboratory work 59.96 ± 3.937; standing household work 61.78 ± 3.675; walking 122.06 ± 6.25; ascending stairs 159.94 ± 5.610 and descending stairs 95.80 ± 6.3. The total daily energy expenditure of the subjects, determined for a period of 7 days, varied between 1620 and 2967 Cal. The average food actually consumed by the subjects was analyzed for fat, protein and carbohydrate to determine the calorific value. The intake varied between 1680 and 2928 Cal/day. Most of the subjects were in apparent positive caloric balance but caloric intake was probably overestimated becauseno correction was made for the caloric value of the excreta. Submitted on October 21, 1958