Description: Propidium Iodide (PI) is a ready-to-use solution for the exclusion of nonviable cells in flow cytometric analysis. PI binds to double stranded DNA by intercalating between basepairs, but is excluded from cells with intact plasma membranes. PI can be used in FL3 for inviability exclusion, but should be analyzed in FL2 when used as a counterstain for FITC Annexin V.