DNA complementary to the rat hypothalamic mRNA coding for the corticotropin-releasing factor precursor (prepro-CRF) has been cloned by screening a cDNA library with a human genomic DNA probe. Nucleotide sequence analysis of the cloned cDNA has revealed that rat prepro-CRF consists of 187 amino acid residues including a putative signal peptide. The CRF and putative signal peptide regions are more highly conserved among rat, human and ovine prepro-CRF than is the cryptic portion.