Alcoholic methylene blue is a methylene blue solution dissolved in ethanol instead of water. Methylene blue is a basic dye mainly used for staining cell structures, especially nuclei, in histological and cytological specimens.

Alcoholic methylene blue solution has several advantages over aqueous methylene blue solution. It offers improved penetration into fatty tissues and can provide better staining of certain structures. Alcoholic methylene blue can also be used to stain air and bone marrow preparations because it offers better dye binding to these materials.

A well-known application of alcoholic methylene blue is the Löffler methylene blue stain, which is used in bacteriology to stain Gram-positive bacteria. It can also be used to stain neurons in histological specimens or to stain blood cells in cytological smears.

Overall, alcoholic methylene blue is a useful staining solution for various applications in histology, cytology, and bacteriology, especially when improved penetration and binding to specific tissues or structures is required.