Used historically as an antimalarial agent, particularly during World War II when quinine was in short supply. It has also been employed in the treatment of certain protozoal infections such as giardiasis and tapeworm infestations. In dermatology, it has been applied in the management of some autoimmune skin conditions like discoid lupus erythematosus. Additionally, it has served as a fluorescent stain in cytogenetics and molecular biology for chromosome banding studies, aiding in the visualization of chromosomal abnormalities. Limited use today due to newer, safer alternatives and potential side effects.