Growth hormone-releasing factor (GRF) is believed to mediate both neural and hormonal control of the release and perhaps synthesis of growth hormone (GH) from the anterior pituitary. Its presence in only minute quantities in the hypothalamus hampered for many years efforts to determine its structure. Recently, two groups independently characterized a peptide from two human pancreatic tumours that possessed GH-releasing activity. Antibodies to this peptide have revealed immunoreactive material in the hypothalamus of several primate species. Furthermore, an apparently identical peptide has now been isolated directly from human hypothalamus. Using both oligonucleotide and antibody screening of a cDNA expression library, we have isolated a recombinant clone encoding human pancreatic GRF (hpGRF) within a larger precursor protein. The nucleotide sequence predicts that processing of GRF from the precursor should generate two additional peptides of unknown function. Restriction analysis of genomic DNA indicates that there is probably a single human GRF gene and suggests that the pancreatic tumour and hypothalamic proteins are encoded by an identical mRNA.