With the change of light source from mercury arc to laser, the cooling system from water cooled to air cooled, and the computer system from simple to sophisticated, the size of the flow cytometer has become smaller and its function expanded in terms of data storage, number of fluorochromes used, and graphic and data display. However, the basic components of a flow cytometer remain the same: the fluid transport system, the optical system the electronic system, and the computer system (1-8)