Small unmyelinated nerves which accompany the blood vessels of the dental pulp have been observed by numerous investigators. It was suggested that such nerves are vaso-regulatory, but there is little direct evidence to support this view, especially in a typically mammalian tooth. The dental pulp of the mandibular canine tooth was exposed without inducing hemorrhage in 8 pentobarbital anesthetized cats. The pulps were transilluminated and observed microscopically during stimulation of the peripheral end of the severed ipsilateral cervical sympathetic nerve. In all cases stimulation at 10 cps., 5 msec. pulses, from 0.3 to 3.0 v resulted in abrupt decrease in flow and decrease in vessel diameter of most of the pulpal vessels. After termination of stimulation vessel diameters rapidly returned to prestimulation or even larger diameters. No parallel changes in systemic blood pressure were noted. Mechanisms underlying the vasoconstriction and a possible post-stimulation increase in blood flow are currently under investigation.