The primary structure of a precursor protein that contains β-neo-endorphin, dynorphin and a third leucine-enkephalin sequence with a carboxyl extension has been deduced from the nucleotide sequence of cloned DNA complementary to the porcine hypothalamic mRNA encoding it. The three peptides are each bounded by Lys–Arg. This precursor protein, like adrenal preproenkephalin and the corticotropin/β-lipotropin precursor, comprises multiple repetitive units and a cysteine-containing ammo-terminal sequence preceded by a signal peptide.