Abstract: Novel polypeptides, polynucleotide sequences, DNA constructs and compositions are provided for the preparation and use of polypeptides associated with naturally occurring polypeptides found in brains. The small molecular weight polypeptides are growth inhibitors for neoplastic cells without inhibiting normal cells. The polypeptides comprise specific regions which are highly conserved, separated by less conserved regions. The polypeptides find use in inhibiting neoplastic growth and detecting receptors for the polypeptides. Antibodies are provided in conjunction with the polypeptides, which may be used together or separately for detecting the presence of the neoplastic cell retarding polypeptides.