Azure II is a metachromatic thiazine dye primarily used in biological staining techniques, including histology, cytology, and hematology. It is a key component in Romanowsky-type stains, such as Giemsa, for differential staining of blood cells, bone marrow, and tissue samples, enabling clear visualization of red blood cells, white blood cells, platelets, and parasites. The dye also stains nucleic acids like DNA and RNA, aiding research in genetics and cellular biology. Additionally, it is employed in pathological examinations to identify abnormal cell structures and support disease diagnosis, such as in leukemia and anemia. Its contrast-enhancing properties make it essential in medical and scientific laboratories.