In single unit recordings from the saphenous nerve in anesthetized cats, afferent units were functionally identified as unmyelinated (C) mechanoreceptors. All units responded to stimulation of the sympathetic trunk with a repetitive discharge which was maintained throughout the period of stimulation. This discharge was asynchronous with respect to efferent activity and was unaffected by brief occlusion of the arterial blood supply. The mechanism underlying the strong excitatory action of the sympathetic system on these afferents is not known although changes in blood flow and temperature can be ruled out. It is suggested that the primary function of these afferents may be to signal conditions within the skin for regulatory purposes rather than to encode external mechanical events.