A mixture of tritiated proline and fucose was injected into the endolymph of one of the membranous labyrinths of each of 5 white king pigeons (Columba livia). The membranous labyrinth was resealed and the animals were allowed to survive for 15 days. Brains and upper parts of the spinal cords were sectioned and processed by standard autoradiographic procedures. Clear labeling was noted in structures usually associated with both the ascending auditory pathways and the ascending and descending vestibular pathways. Vestibular structures ipsilateral to the injected labyrinth which contained heavy labeling were Scarpa's ganglion and all 6 vestibular nuclei. No labeling was noted in the contralateral Scarpa's ganglion and sparce, if any, labeling was noted in the contralateral vestibular nuclei. Contralateral structures associated with ascending vestibulo-ocular pathways which contained heavy labeling were the medial longitudinal fasciculus, abducens nucleus, trochlear nucleus, and two parts of the oculomotor nucleus--the dorsolateral part and the ventromedial part. Less heavily labeled ipsilateral vestibulo-ocular-related structures included the medial longitudinal fasciculus, abducens nucleus and the ventrolateral edge of the trochlear nucleus. The dorsomedial part of the oculomotor nucleus was heavily labeled on the side ipsilateral to the injected labyrinth. Slight, if any, labeling was noted in either the ipsilateral or contralateral brachium conjunctivum or regions corresponding to the mammalian ascending tract of Deiters. The medullary core of most folia but primarily the medullary core and granular areas of folia IX and X of the cerebellum were labeled.(ABSTRACT TRUNCATED AT 250 WORDS)