Pyronin B is a synthetic xanthene dye, closely related to Pyronin Y. It is a cationic dye that exists as a red powder and is soluble in water and ethanol. Structurally, it is characterized by its amino-substituted xanthene core, which is responsible for its fluorescent properties. Its primary application is in the field of life sciences and histology as a fluorescent stain and biological tracer. Pyronin B is commonly used in combination with other dyes, such as methyl green in the Methyl Green-Pyronin stain, for the differential staining of DNA and RNA in tissue sections. It selectively binds to RNA, producing a pink to red fluorescence under appropriate illumination, which is crucial for studying cellular nucleic acid distribution and for identifying plasma cells and other RNA-rich structures. It also serves as a fluorescent probe in flow cytometry and other cytological techniques. While its main use is biological, its properties as a colored, cationic organic compound also make it relevant in analytical chemistry as a pH indicator and a redox indicator in certain titrimetric methods. It is important to handle Pyronin B with care, using appropriate personal protective equipment, as it may cause irritation upon contact with skin, eyes, or if inhaled.