Azure A is an organic compound with the chemical formula C<sub>14</sub>H<sub>14</sub>ClN<sub>3</sub>S. It is a light blue to dark blue dye. It is used as a screening test for mucopolysaccharides. It can also be used to stain lysosomes in blood smears, and is often used in Giemsa stain. It's formed via oxidation of Methylene blue.