A DNA fragment containing the human corticotropin releasing hormone (CRH) gene, along with 9 kb of upstream and 4 kb of downstream sequences, was isolated from a human genomic DNA library. Nucleotide sequence analysis of the proximal 918 nucleotides 5' flanking the putative major mRNA start site of the human gene and comparison to the 866 nucleotide long homologous ovine sequence, revealed that this region of the CRH gene consists of two distinct areas with different degrees of homology, varying from 72% to 94%. The putative functional features of the human sequence were identified. Many, but not all, features were conserved in the ovine sequence. The highly conserved nature of the regulatory region of this gene makes it a good candidate for tracing possible related genetic defects of the hypothalamic-pituitary-adrenal (HPA) axis.