In many areas of immunology it is desirable to be able to track particular cells throughout an assay, whether it be in vivo or in vitro. There are two classes or reagents used for this purpose-general protein labels (reactive compounds that form random covalent bonds with amino groups on cellular proteins) and general membrane labels (lipophilic compounds that partition stably but non-covalently into the plasma membrane). The fluorescein derivative, carboxyfluorescein diacetate succinimidyl ester, CFDA-SE (general protein label), has been found to be particularly well suited for the purpose of cell tracking. Once labeled, cells can be tracked both in vivo and in vitro. Moreover, due to the randomness of the labeling, cells undergoing division maintain half of the staining intensity of the parent cell. This halving of the staining intensity additionally allows for monitoring of cells undergoing division for 6-8 consecutive cycles.