Prussian blue is used to demonstrate ferric (+3 charge) iron in tissues. A liver biopsy is used to diagnose both hereditary hemochromatosis and hemosiderosis. Hemochromatosis and hemosiderosis are both conditions that cause the liver to accumulate excess iron. Iron can be seen as a brown pigmentation on a hemotoxylin and eosin (H&E) stained tissue slide but may be difficult to distinguish from other pigments. Therefore, an iron stain is commonly used to positively identify iron in the liver. The mode of action for the Prussian blue iron stain is to treat the tissue with an acidic solution (hydrochloric acid). Ferric (+3 charge) iron that is present in the tissue will react to form Prussian blue which is visualized as an insoluble blue pigment. In the image, a liver biopsy stained with Prussian blue is used to demonstrate ferric iron in a patient with hemochromatosis.