As a preliminary approach to the understanding of heat regulation during anesthesia, the effect of the inhibition of sweating was studied. Seven healthy young males fasted 14 hrs., and then were placed, lightly clothed, in an insulated room with temp. and humididity stabilized at 96OF and 55%, respectively, for 4 hrs. Body wt., rectal temp., pulse rate and blood pressure were recorded. One week later the same subjects underwent an identical experience 15 min. after an injn. of 0.4 mg. of scopolamine hydro-bromide. Two subjects were exposed to this environment again one week later, and scopolamine was given as described and repeated 2 hrs. later. The unmedicated subjects sweated profusely. 0.4 mg. of scopolamine caused absence of sweating during the first 2 hrs. A 2d dose of scopolamine inhibited sweating completely. Rectal temp. and blood pressure were not altered in any case. Scopolamine decreased sweating by 35%. Such inhibition of sweating may be a factor contributing to hyperthermia during surgical operations if normal sweating is impaired further by illness or if heat cannot be lost by other routes.