Thymidine is widely used in molecular biology and medical research as a key component in the synthesis of DNA. It is essential for studying DNA replication and cell proliferation, often incorporated into DNA during cell division to track or measure cell growth. In cancer research, thymidine analogs are employed to inhibit DNA synthesis in rapidly dividing cancer cells, serving as a therapeutic agent. Additionally, it is used in radioactive labeling techniques, such as tritiated thymidine, to trace DNA synthesis and repair processes in experimental studies. Thymidine also plays a role in antiviral therapies, where its analogs are used to disrupt viral DNA replication in infections like HIV and herpes.