During apoptosis, phosphatidylserine (PS) is translocated from the cytoplasmic face of the plasma membrane to the cell surface. Annexin V has a strong, Ca2 -dependent affinity for PS and therefore is used as a probe for detecting apoptosis. The unlabeled Annexin V reagent can be conjugated to any tag of choice for detection of apoptosis. The reagent can also be used in competition binding experiments with tagged annexin V conjugates. Annexin V-FITC, -Cy3, -Cy5, -EGFP, -PE, -Biotin Labels are also available.