Methylthionine chloride, also known as methylene blue, is a dye that is used in medical applications for its antiseptic and analgesic properties. Synonyms for methylthionine chloride include methyl blue, aniline water blue, and tetramethylthionine chloride. The compound is also commonly referred to as simply "blue dye" or "MB," and is used in a variety of laboratory tests and procedures. It has been used in research regarding Alzheimer's disease and has shown potential as a treatment for depression. Its blue color makes it useful in staining tissue samples and for visualization in microscopy. Overall, methylthionine chloride holds a significant place in medical and scientific communities.