Annexin V cannot be used to stain fixed cells or tissues. After staining with Annexin V and washing, cells can be fixed with 2% formaldehyde. Annexin V stainingis calcium dependent, we recommend including 2.5 mM calcium in the buffer and formaldehyde solution used for washing and fixation. Annexin V binds to a phospholipid in the plasma membrane, therefore staining is not compatible with alcohol fixation or detergent permeabilization.