Determinations of basal metabolism are widely used in the clinical study of obese patients, apparently in the expectation of arriving at some understanding of the underlying disturbance. Von Noorden 1 classified obesity as exogenous and endogenous and defined endogenous obesity as characterized by a lowered metabolism or, as he called it, "Verlangsamung der Zersetzungsenergie der Zellen." He stated that obesity of the endogenous type is rare. Since hypofunction of the thyroid gland is associated with a depression of the basal metabolism, the conclusion is frequently drawn that a low basal metabolic rate in an obese person is indicative of hypothyroidism.The term basal metabolic rate is ambiguous, and its inconsistent use has caused much confusion. Many authors designate by basal metabolic rate the percentage deviation of the observed value from some normal standard. The most widely accepted standard uses surface area as the unit of comparison. In numerous clinical papers in which the diagnosis "obesity of primary or secondary hypothyroid origin" is based on the observation of a low basal metabolic rate, inadequate information is given as to the method of computation. Workers who have critically evaluated the significance of standards for the result have not recorded a lowered metabolic rate or even found an elevation corresponding to the excess in weight.2In dealing with growing children, who are constantly changing sub¬ jects, the interpretation of metabolic tests is even more difficult. The