During the sixties, investigational efforts around automated cytology, biophysics, computer processing, flurochrome chemistry and monoclonal antibody technology created the new field of flow cytometry, giving thus the ability for scientists and clinicians to make biological measurements in viable cells and fixed tissues. The initial applications of this new technology to the problems of cellular biology, pathology, immunology and hematology was mainly done in research laboratories due to the high cost and sophisticatin of the first instruments in use. The recent development of smaller, more compatible systems for the clinical laboratory have made the flow cytomater a very valuable tool for up-to-date pathological diagnosis. Flow cytometry can be used to identify and rapidly count different kinds of cells in the heterogeneous structure of a tissue sample. The ability to characterize a particular subset of cells depends on labeling them with fluorescent markers that identify specific cellular components like DNA, RNA, mitochondria and a whole repertoire of intracellular components like DNA, RNA, mitochondria and a whole repertoire of intracellular and membrane proteins