The May-Grünwald eosin solution consists of a mixture of the dyes eosin Y, eosin B and methylene blue. Eosin stains acidophilic structures red, while methylene blue stains cell nuclei, nucleic acids, chromosomes, and basic areas of cells.

May-Grünwald eosin solution is commonly used to stain blood smears and bone marrow preparations. In Romanowsky staining, which includes May-Grünwald eosin solution, May-Grünwald solution is first used as the primary stain, followed by eosin solution as the secondary stain. The combination of these dyes allows differentiation of various cell structures and cell types, such as red blood cells, white blood cells, platelets, and various bone marrow cells.

In cytology and histology, May-Grünwald eosin staining is known for its excellent resolution and contrast, making it a valuable method for examining blood and bone marrow specimens. The combination of different dyes in the May-Grünwald-Eosin solution allows to distinguish cell nuclei and nucleic acids as well as acidophilic structures such as cell plasma proteins, mitochondria, the smooth endoplasmic reticulum, collagen and keratin.