Buffer for use with the BioVision's multi-color bulk annexin V reagents including annexin V-FITC (Cat# 1001-1000), annexin V-EGFP (Cat.# 1004-1000), annexin V-Cy3 (Cat.# 1002-1000), annexin V-Cy5 (1013-1000), annexin V-Biotin (Cat.# 1003-100), annexin V-PE (1014-1000) and unlabeled annexin V (1005-100). 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 serves as a probe for detecting apoptosis. BioVision's 1X Annexin V Binding Buffer is ready to use for annexin V binding assay to detect PS exposure during apoptosis.