The Romanowsky-type stain variants such as those originally described or modified by numerous authors are routinely used for the staining of blood and bone marrow films. A two-component stain is required to produce the so-called Romanowsky-Giemsa effect. Hence, all these stains contain a mixture of methylene blue and related thiazin dyes and eosin. The thiazin component must be azure B and the eosin component may be eosin Y or one of the corresponding erythrosins. Azure B (methylene azure B) is formed by the oxidation of methylene blue. Best staining is obtained by use of a more dilute staining solution with a longer incubation time. Differentiation can be achieved in two steps: (a) with dilute acetic acid to remove excess blue staining, and (b) 95% ethanol to remove excess eosin. This is difficult to standardize, and sections must be processed under microscopic control.