Flow cytometry is one of the powerful tools for the investigators in immunological research involved in studying various immune cells. One of the main advantages of this technique is that is capable of multi-parameter measurements that can be accomplished on a single-cell basis. As a result of the advances in the flow cytometry researchers can now decrypt the phenotypes of several cell subsets in ways that were not possible using traditional assays, such as Western/immunoblotting, microarrays and enzyme-linked immunosorbent assays.