TB Carbol Fuchsin Kinyoun reagent is used in staining acid-fast bacteria such as Mycobacteria and Nocardia strains that cannot be stained using simple dyes (or provide different results if successfully stained). Cellular wall of the Mycobacteria strain contains waxy substance – mycolic acid. Those are beta-hydroxy carboxylic acids with chains containing up to 90 carbon atoms. Its resistance to acidity is associated with mycolic acid chain length. TB Carbol Fuchsin contains phenol that allows the dye to penetrate the mycobacterium cell wall by heating, and the dye is almost impossible to remove from the cell during decolorization. The reagent is used for special staining according to Ziehl-Neelsen which is the most renowned and most widely used method of identification of tuberculosis bacteria.