Recently, we have elucidated the primary structure of bovine adrenal preproenkephalin by determining the nucleotide sequence of cloned DNA complementary to its mRNA1. The structure of most of this precursor molecule has also been deduced by Gubler et al.2 using cDNA sequencing in conjunction with protein sequencing. Bovine preproenkephalin contains four copies of methionine-enkephalin3 (Met-enkephalin) and one copy each of leucine-enkephalin3 (Leu-enkephalin), Met-enkephalin-Arg6-Phe7 (ref. 4) and Met-enkephalin-Arg6-Gly7-Leu8 (refs 1, 2, 5). The region containing the repeated enkephalin and extended enkephalin sequences, which are each bounded by paired basic amino acid residues, is connected with a cysteine-containing amino-terminal sequence preceded by a signal peptide6. We have now studied the relationship between the repetitive structure of preproenkephalin and the structural organization of its gene by cloning a human genomic DNA segment containing the entire gene. We find that the general organization of the preproenkephalin gene is strikingly similar to that of the gene encoding the common precursor of corticotropin (ACTH) and β-lipotropin (β-LPH)7-9 (alternatively designated preproopiomelanocortin), another multi-hormone precursor. Furthermore, the complete mRNA and amino acid sequences of human preproenkephalin have been deduced from the corresponding gene sequence.