Congo Red is used to stain amyloid within tissues. The stain can be used to see the presence of amyloidosis. It can also be used to stain bacteria- specifically virulent serotype 2a Shigella flexneri. Thicker sections (8-10 microns) should be used for staining.

Results: Amyloid deposits will stain a salmon colour or bright red, while background tissue will remain light pink, nuclei will stain blue.