Staining Solutions for DNA Analysis of Mammalian Cells: The fluorescence inside the cell nucleus can be easily detected using flow cytometry. The amount of DNA for cell populations can be studied regarding: a) the cell cycle and b) the ploidy level. In growing tissue, the DNA amount per cell is correlated to certain cell cycle phases of replication of chromosomes. Three different phases can be distinguished: G1, S, G2M (G1: normal DNA content = 2c, S: DNA synthesis, G2M: double DNA content = 4c and mitosis). Mammalian somatic cells are usually diploid with a specific genome size related to the number and individual size of chromosomes. This is in contrast to neoplastic cells, which tend to have abnormal and aneuploid DNA contents. Differences in the genome size usually occur as chromosome abnormalities (different karyotypes). Ploidy levels and cell cycle stages can be detected with Partec flow cytometers by high resolution DNA measurements within differences of 1% compared to the normal cellular DNA content. The Partec FCM instruments, in combination with Partec DNA reagents, can obtain very low CV values (lower than 1 %) for various cell samples.