The human 8.5 H probe was isolated from a human cerebellum cDNA library with a probe corresponding to the coding region of the murine 8.5 M cDNA. This cDNA isolated from a murine cDNA library constructed from newborn cerebral hemispheres was selected because of its strong expression in embryonic neurons. Consequently the corresponding human gene could be a candidate for hereditary neurodegenerative diseases. The human 8.5 H gene was assigned by somatic hybrid analysis to chromosome 5; this chromosome contains the gene(s) for spinal muscular atrophy (SMA), a group of heritable degenerative diseases that selectively affect the anterior horn motor neuron of the spinal cord. The localization by in situ hybridization of 8.5 H on 5q35 excluded the possibility that this gene is identical to SMA. The SMA gene(s) was (were) known, from linkage analysis, to be in a region (5q11.2-q13.3) very distant from 5q35.