4-Azidosalicylic acid finds its primary application in the field of biochemical research, particularly in photoaffinity labeling. This technique is used to study protein-ligand interactions by covalently attaching the compound to a target protein upon exposure to ultraviolet light. The azido group in the molecule serves as a photoreactive moiety, enabling the formation of stable bonds with nearby amino acids in the protein. This allows researchers to identify and map binding sites, providing insights into the molecular mechanisms of biological processes. Additionally, it can be utilized in the development of probes for investigating enzyme active sites or receptor binding domains, contributing to drug discovery and design.