Electrolytic lesions were placed in the medial cerebellar nucleus in tree shrews (Tupaia glis) or in fibers issuing from this nucleus. Brains and spinal cords were processed according to Fink-Heimer procedure following survival times of 2-7 days. In control animals lesions were placed in the cerebellar cortex and, in one case, in the olfactory bulb. Degenerating fibers were seen entering the cervical spinal cord and continuing to thoracic and lumbar levels. The projection is relatively profuse in the cervical cord, becoming sparse as the fibers proceed to more caudal levels. Fibers run in the lateral funiculus, predominantly contralateral to the lesion. Some fibers are observed to travel directly through the intermediate gray matter of the spinal cord. Preterminal degeneration is seen primarily in the intermediate gray of the spinal cord. Results are discussed in relation to typical locomotor behavior of tree shrew.