Summary.No evidence was found for the existence of a sympathetic vasodilator innervation to the skin of the hind limbs or the ear of the dog.Nor‐adrenaline has a pronounced vasoconstrictor action on cutaneous vessels. The observation agrees with the idea that the substance might be the transmitter at vasoconstrictor nerve endings.Adrenaline has a pure vasoconstrictor action on cutaneous vessels, even in low concentrations.Acetylcholine has a pronounced vasodilator action on cutaneous vessels. Thus it cannot be excluded as a possible transmitter at cutaneous vasodilator nerve encling