Romanowsky stain is a staining technique used in hematology and cytopathology to differentiate cells for microscopic examination in pathological specimens, especially blood and bone marrow films, and to detect parasites such as malaria within the blood. The staining technique is named after the Russian physician Dmitri Leonidovich Romanowsky, who was one of the first to recognize its potential for use as a blood stain. The value of Romanowsky staining lies in its ability to produce a wide range of hues, allowing cellular components to be easily differentiated. This phenomenon is referred to as the Romanowsky effect, or more generally as metachromasia. Romanowsky-type stains are also used for the staining of cytopathologic specimens such as those produced from fine-needle aspirates and cerebrospinal fluid from lumbar punctures. The stains that are related to or derived from the Romanowsky-type stains include Giemsa, Jenner, Wright, Field, May–Grünwald, and Leishman stains.