The ninth nerve was severed and the rat carotid body studied in the light and electron microscopes and after formaldehyde-induced fluorescence for its catecholamine content from 3 weeks to 13 months after operation. Minimal changes in the carotid body were observed. Hyperthrophy of the capsule cell was noticed up to about 2 months, after which time these cells appeared normal. Lysosomes in the capsule cells occurred more frequently and were larger than in normal carotid bodies. Discernible pathological alterations did not occur in the glomus cells, despite the absence of afferent terminals upon them. Atrophy of the carotid body was not noticed. The catecholamine content of the denervated carotid body was comparable to its innervated control and no nerve terminals were found on the glomus cells. Autonomic ganglion cells intrinsic to the carotid body varied in number from 1 to 8 and in location. The glomus cells do not receive any significant autonomic innervation, and the ganglion cells in the carotid body, perhaps sympathetic, probably innervate blood vessels. It is concluded that deafferentation has minimal morphological effects on the carotid body. The reactions of other receptor cells to deafferentation are compared with those of the glomus cells.