How is propidium iodide used in flow cytometry?

Propidium iodide is used in several different applications in flow cytometry. It is used to assess cell viability, to provide information about the cell cycle, and the DNA content of the given population. PI fluorescence intensity provides quantitative information about the DNA content of cells. Cells with intact plasma membranes exhibit low fluorescence, while dead or damaged cells uptake PI and exhibit higher fluorescence.