This stain is specific for lipids. Sudan black B stains a variety of lipids, including neutral fat, phospholipids, and sterols.
Normal granulocyte precursors show increased sudanophilia that corresponds roughly to the number of granules. Promyelocytes contain a few sudanophilic granules, and mature polymorphonuclear neutrophils contain large numbers of sudanophilic granules. Eosinophil granules are also sudanophilic, especially on the edge. Monocytes may be unstained or may contain a few discrete sudanophilic granules. Macrophages often contain sudanophilic material.
In general, Sudan black B stain is similar to the peroxidase reaction in distinguishing acute lymphocytic leukemia from acute myelogenous leukemia.