Rat carotid bodies transplanted into the anterior chamber of the eye were studied by electron microscopy. Chief and sustentacular cells and a few ganglion cells survived for 3 months and maintained cytological characteristics similar to those in the intact carotid body. The transplant contained many fenestrated capillaries. Chief cells at the periphery of the cell cluster had long cytoplasmic processes which projected into the stroma of the iris. The cell processes became incorporated into bundles containing nerve fibres, which were enveloped by a perineurial sheath. Three types of nerve fibres were identified in the explant. Type I and type II nerve fibres (presumptive cholinergic and adrenergic, respectively) were enclosed by sustentacular and satellite cells. Most of the nerve fibres were completely separated from chief cells and ganglion cells by sustentacular and satellite cells. A few nerve fibres made direct apposition to chief cells and ganglion cells, where some nerves were presynaptic to them. Type III nerve fibres derived from myelinated nerve fibres were also enclosed by sustentacular and satellite cells.