The presence of a multitude of DNA strand breaks resulting from fragmentation of nuclear DNA by the caspase-activated DNase is one of the most chaacteristic features of apoptotic cells (1 ,2 ). A widely used methodology to detect apoptotic cells, thus, relies on labeling DNA strand breaks in situ, within the nuclear chromatin, either with fluorochromes (3 –5 ) or absorption dyes (6 –8 ). The overview of the techniques (TUNEL techniques), which were developed independently by Gavrieli et al., (6 ) and by us (3 –5 ) is presented in Chapter 3 . One advantage of strand break labeling with fluorochromes is that such cells can rapidly be analyzed by flow cytometry. When cellular DNA content also is measured in these cells, the bivariate analysis of such data provides information about DNA ploidy or the cell cycle phase specificity of apoptosis (3 ,9 ).