The central distribution of primary afferent fibers of the eighth cranial nerve was analyzed in the common South American caiman by comparison of patterns of anterograde fiber degeneration resulting from differential lesions of the nerve. Degenerating fibers from the papilla basilaris project only to ipsilateral nuclei angularis, magnocellularis medialis and lateralis, and to the neuropil above laminaris. Discrete electrolytic lesions suggest a spatial ordering of this auditory projection within the ''cochlear'' nuclei. Primary afferents from vestibular endorgans distribute to six nuclei ipsilaterally: ventrolateralis, ventromedialis, descendens, tangentialis, dorsolateralis, and a previously unrecognized group labeled here ''dorsomedialis''. Analysis of differential degeneration patterns indicate that nerves from specific semicircular canals project to restricted regions within the vestibular nuclear complex. For example, the dorsal subdivision of ventrolateralis receives fibers chiefly from the posterior crista, while the anterior and horizontal canal nerves project to the ventral and medial subdivisions. Primary vestibular fibers also project bilaterally to the granular layer of the cerebellum at more rostral levels.