Flow immunophenotyping is a method used to analyze blood, bone marrow or other tissues in order to determine the expression level of certain proteins on the component cells. It is most useful in the diagnosis of leukemia and lymphoma. Cell suspensions are mixed with a cocktail of fluorescently-labeled antibodies and then analyzed, one cell at a time, using flow cytometry. Briefly, a laser light is used to probe the individual cells in order to calculate their size (forward scatter), internal complexity (side scatter) and the presence of the antigen-bound antibodies used in the cocktail.