Seleno-D,L-ethionine is a selenium analog of methionine, where the sulfur atom is replaced by selenium. This structural similarity allows it to be used in biological and medical research to study selenium-related biochemical processes. It serves as a selenium donor in experiments to track and understand selenium incorporation into proteins, enzymes, and biological systems. Additionally, it is utilized in cancer research to explore effects on tumor growth and cellular pathways, as well as in nutritional studies investigating selenium's impact on health, disease prevention, deficiency, accumulation-related disorders, and cellular protection against oxidative stress. It acts as a tool in laboratory assays to trace selenium distribution and metabolism in cells and tissues.