The distribution of lateral funicular and cerebral corticofugal fibers to the dorsal column, Z and X nuclei were studied in the prosimian primate Galago senegalensis. Lesions of the lateral funiculus resulted in a differential distribution pattern of preterminal degeneration within the nuclei studied. In the nucleus gracilis, spinal lesions produced moderate amounts of debris in ventral cell nest and rostral areas. Diffuse degeneration was present in both the dorsal cell nest area of the nucleus gracilis and the rostral nucleus cuneatus. Extremely dense debris was present within both ipsilateral Z and X nuclei. Cortical ablations of predominantly hind-limb motor-sensory areas resulted in degeneration throughout most of the longitudinal and transverse extent of the contralateral dorsal column nuclei. Degeneration appeared to be more concentrated in ventral nuclear areas. The distribution of cortical fibers to the rostral gracile and Z nuclei was essentially the inverse of that observed for lateral funicular fibers. The contralateral nucleus Z received only a sparse corticobulbar input while the rostral gracile contained more moderate amounts of preterminal degeneration. The results are in agreement with previous reports on the morphology and fiber connections of the dorsal column, Z and X nuclei in Galago and other animals. They support the concept that the Z and X nuclei are functional components of the dorsal column nuclear system.