The present invention relates generally to Activity Dependent Neurotrophic Factor III (ADNF III), also known as Activity Dependent Neuroprotective Protein (ADNP). More particularly, the present invention relates to nucleic acid sequences encoding ADNF III polypeptides; ADNF III polypeptides encoded by such nucleic acid sequences; antibodies to ADNF III polypeptides; and methods of using such ADNF III polypeptides for the treatment of neurological deficiencies and for the prevention of cell death associated with (1) gp120, the envelope protein from HIV; (2) N-methyl-D-aspartic acid (excito-toxicity); (3) tetrodotoxin (blockage of electrical activity); and (4) .beta.-amyloid peptide, a substance related to neuronal degeneration in Alzheimer's disease.