This method is convenient because it does not require removal of cell culture medium, which can result in loss of detached apoptotic cells (see Figure 1). It also eliminates the need to centrifuge suspension cells before staining. Take care to gently mix the medium immediately after adding Annexin V solution to each sample to avoid uneven staining from transient high local probe concentration, or cell disruption by overly vigorous pipetting. Adding undiluted (50 ug/mL) Annexin V stock solution directly to cells is not recommended.