Observations on the neural regulation of the human sweat apparatus may help to clarify two outstanding problems concerning the functioning of the skin. It has been known since the work of Kuno andhis school (1956) that the emotive type of sweating is confined to specific area-s of the skin, palms, soles, axillae and limited parts of the face. These commence sweating possibly within a second after the application of a stimulus, such as mental arithmetic, discussion of an embarrassing topic, or physical exercise. Other areas of the skin surface do not show any trace of sweating in response to such stimuli at normal ambient temperatures up to 260 C, or higher, in most individuals. The responses to thermal stimuli, however, show a converse relationship. The general body surface responds primarily to thermal stimulation. When the ambient temperature around the subject is raised at a certain point there is a sudden onset of sweating. The emotive sweating areas, palm and sole, commence sweating later, and at a higher temperature than the other parts of the body.The sweat response of the emotive areas is accompanied by skin electrical changes, extensively used in psychological studies as a measure of arousal activity, though the exact nature of the physical relation between sweating and these electrical events has not yet been clarified. At high ambient temperatures, e.g. above 30°C, emotively induced sweating is seen on the general body surface (Kuno, 1956). The observations to be described here provide information about the nature of the mechanism causing this change in the sweating behaviour of the body surface.The work of Fox & Hilton (1958) on the control of blood flow to the skin has demonstrated the importance of the sweat mechanism in vasodilatation. These experiments showed that an enzyme appeared to be released in the sweat itself, causing the formation of bradykinin in the skin, which then brought about vascular dilatation by direct action. However, it was noted by Fox & Hilton (1958) that there was a small discrepancy between the incidence of vasodilatation and sweating. Vascular dilatation occurred