BioGnost’s Eosin Y 2% is an aqueous reagent which is commonly used as a contrast dye for hematoxylin in the histological staining method, the hematoxylin and eosin (HE) staining. This method achieves better cellular structure visualization and differentiation. The microscopic samples’ nuclei are stained blue using hematoxylin, then they are stained various shades of pink using cytoplasm eosin. Eosin Y is a fluorescein derivative. As color powder it can be used as a reagent mixture often used in histological, but also in cytological methods of staining, such as the Papanicolaou method in exfoliative cytology or for creating Romanowsky dyes. Eosin Y is anion dye which stains erythrocytes bright red, and it also stains basic cellular components, such as cytoplasm, collagen, and muscle fibers.