Propidium Iodide (PI) is the most commonly used dye for DNA and cell cycle analysis for flow cytometry. The PI binds to DNA by intercalating into the double stranded macromolecule. PI also binds to RNA, and is necessary to remove the RNA with a nucleases treatment (RNase) for optimal DNA resolution. The quantification of the content DNA, it permit us to know the distribution of a cell population along the different phases of the cell cycle. In the analyses of a cell population by flow cytometry using dyes for DNA, the quantity of binded dye is proportional to the quantity of DNA. The analyses of cell cycle by flow cytometry are represented in fluorescence intensity histograms for it probes specific of DNA. The cells of mammalian are characterized for having three populations or definite regions, cells in G2 and M phases of the cell cycle that have double DNA content of those in G0 and G1 phases, and a region correspond to cells in phase S.