Azure II is primarily utilized in biological staining, particularly in histology and cytology. It is commonly used in combination with other dyes to enhance the contrast of cellular components under a microscope. This dye is effective in highlighting specific structures within tissues, making it valuable for diagnostic purposes in medical and research laboratories. Additionally, Azure II is employed in the staining of blood smears to differentiate various types of blood cells, aiding in the identification of abnormalities or diseases. Its application extends to the study of nucleic acids, where it helps in visualizing DNA and RNA in cellular samples.