The Annexin V-EGFP/PI Cell Apoptosis Kit provides a rapid and sensitive method for early apoptosis detection. In normal cells, the membrane phospholipid phosphatidylserine (PS) is located on the cytoplasmic surface of the membrane. In apoptotic cells, PS is translocated from the inner to the outer leaflet of the plasma membrane, thereby exposing PS to the external cellular environment. The EGFP-conjugated Annexin V, a Ca2+ dependent phospholipid-binding protein, can bind specifically to the exposed PS. Propidium iodide (PI) is a nucleic acid binding dye, which binds tightly to the nucleic acids in the cells and stains the cells with red fluorescence. PI is impermeant to live cells and early apoptotic cells, so the combination of Annexin V-EGFP and PI staining allows the differentiation among different stage of apoptotic cells and necrosis cells. Compared with FITC, EGFP is brighter and more photo-stable. Because Annexin V-EGFP is a fusion protein with a 1:1 binding ratio of EGFP to PS, this kit can also be used for quantitative detection.