In addition to the preganglionic axons which innervate the superior cervical ganglia, the cervical sympathetic trunks of the rat contain axons of ganglionic neurons. Following the application of horseradish peroxidase to the cut cervical sympathetic trunk just caudal to the superior cervical ganglion, a population of approximately 300 labeled neurons was found in the inferior and middle cervical ganglia. The labeled neurons were localized primarily in the more rostral regions of these ganglia. The axons of most of these neurons entered the superior cervical ganglion, passed through it, and left via the external carotid nerve. The relevance of these observations to physiological studies on the cervical sympathetic nervous system is discussed.