The GenScript Double Stain Apoptosis Detection Kit (Hoechst 33342/PI) provides a rapid and convenient assay for apoptosis based upon fluorescent detection of compacted chromatin in apoptotic cells. This kit contains two ready-to-use dyes bound to DNA. Hoechst 33342, a type of blue-fluorescence dye (excitation/emission maxima ≈350/461 nm when bound to DNA), stains the condensed chromatin in apoptotic cells more brightly than normal chromatin. Propidium iodide (PI), a red-fluorescence dye (excitation/emission maxima ≈535/617 nm when bound to DNA), is only permeant to dead cells. The staining pattern resulting from the simultaneous use of these dyes makes it possible to distinguish normal, apoptotic, and dead cell populations by flow cytometry and fluorescence microscopy.