A novel polypeptide, designated neurotrophic factor-4 (NT-4), has been identified by PCR amplification of human genomic DNA. Provided herein is nucleic acid encoding NT-4 useful in diagnostics and in the recombinant preparation of NT-4. Also provided herein are nucleic acids encoding naturally occurring amino acid sequence variants of NT-4, designated NT-4.beta., NT-4.gamma., and NT-4.DELTA.. The neurotrophic factors of the invention are useful in the treatment of nerve cells and in diagnostic assays.