Propidium iodide (or PI) is an intercalating agent and a fluorescent molecule with a molecular mass of 668.4 Da that can be used to stain cells. When excited with 488 nm wavelength light, it fluoresces red. PI binds to both DNA and RNA, so the latter must be removed by digestion with ribonucleases. The content of DNA as determined by flow cytometry, can reveal useful information about the cell cycle and the proteins involved in the regulation of the cell cycle. This reagent may be used to analyz