Adrenocorticotropic hormone fragment 18-39 is primarily used in research settings to study the structure and function of the adrenocorticotropic hormone (ACTH). It helps in understanding the specific regions of ACTH that are responsible for its biological activity, particularly its role in stimulating the adrenal cortex to produce cortisol. This fragment is also utilized in immunological studies to investigate antibody interactions and epitope mapping, aiding in the development of diagnostic tools and therapeutic agents targeting ACTH-related pathways. Additionally, it serves as a valuable tool in biochemical assays to explore peptide hormone signaling and receptor binding mechanisms.