This hypophysiotropic peptide was isolated from human hypothalamic-hypophysial tissues. Within this 1 to 29 amino acid GRF fragment, amino acids 13 to 21 are more important than 24 to 29 for high affinity receptor binding. Structure–activity studies show that hpGRF(1–29)-NH2 has full intrinsic activity and potency in vitro as the full length GRF in stimulating growth hormone release.