Sudan Black B stain. Blood film. Acute myelogenous leukemia with minimal maturation. Note staining of myeloblasts with black reaction product. This stain identifies leukemic myeloblasts in contrast to leukemic lymphoblasts and is sometimes positive when the peroxidase stain is not. Very rare cases of acute lymphoblastic leukemia have been described with a positive reaction to this stain, but it is generally a reliable means of establishing a myelogenous phenotype.