The effects of a small dose (3-6μg/kg) of subcutaneously administered adrenaline on thermal sweating were studied while subjects were at rest and during or after exercise by means of continuous monitoring by resistance hygrometry of the sweat rate in the forearm area.In most cases, the sweat rate either decreased or did not change significantly following the adrenaline injection, however, among athletic subjects it showed a mild increase in a few cases, mostly during or after exercise. In the area receiving the intradermal injection of an α-adrenergic blocking agent, tolazoline, phentolamine or dihydroergotoxine, subcutaneous adrenaline consistently caused an increase in sweat rate. Adrenaline (15 μg) was injected intravenously with similar results. Noradrenaline was used in place of adrenaline in some cases, and the results were essentially the same as, but less distinct than, those with adrenaline. The results indicate that a small dose of subcutaneous adrenaline has dual effects, with the sweat-inhibitory effect generally predominating over the sweat-facilitatory one, with occasional exceptions in association with exercise and/or physical training. The former effect is largely secondary to its vasoconstrictive effect, whereas the latter appears to be secondary to its systemic effects, such as central and calorigenic ones. It is concluded that adrenaline within a physiological range exerts no direct action on human eccrine sweat glands.