One of the hallmarks of the early stages of apoptosis is the redistribution of membrane phospholipids such as phosphatidylserine and phosphatidylethanolamine from the inner to outer leaflet of the membrane bilayer where they are exposed on the cell surface. Externalization of phosphatidylserine residues to the outer plasma membrane leaflet allows their detection via their high affinity for annexin V, a phospholipid binding protein. Cayman's Annexin V Assay Kit employs a FITC-conjugated Annexin V as a probe for phosphatidylserine on the outer membrane of apoptotic cells. Apoptotic cells bound with fluorochrome-labeled Annexin V can be visualized using fluorescence microscopy or flow cytometry. The reagents provided in the kit are sufficient to run 500 samples when using a 96-well plate format.