Bismarck brown Y

Bismarck brown Y is a diazo dye. It is used in histology for staining tissues. It stains acid mucins to yellow color. It can be used with live cells. It is also used to stain cartilage in bone specimens, as one of Kasten's Schiff-type reagents in the periodic acid-Schiff stain to stain cellulose, and in Feulgen stain to stain DNA.

It was more common in the past; today it is partially replaced by other stains.

Bismarck brown Y is a constituent of Papanicolaou stains.

It can also be used as a counterstain for Victoria blue R for staining of acid-fast microorganisms.