Dehydrogenase enzyme cytochemistry of unfixed leucocytes

An inert, synthetic, sucrose polymer (Ficoll) has been found to have a protective effect on leucocytes during incubation for cytochemical reactions at 37 degrees C. This permits enzyme cytochemistry to be performed on unfixed bone marrow and peripheral blood smears, and on leucocytes cultured in vitro, thus avoiding enzyme inhibition by the use of a fixative. The technique is suitable for the demonstration of both cytoplasmic and intramitochondrial dehydrogenase enzyme activity.