The rapid and highly quantitative nature of flow cytometric cell cycle analysis for determining the proportion of apoptotic cells in a population makes it the method of choice for a variety of studies requiring quantitative information about cell death. Furthermore, by employing multiparameter analysis including phenotypic labeling, FACS makes it possible to study apoptosis in specific subsets of cells within a heterogeneous population. Live sorting of cells in the apoptotic region offers the possibility of studying the effects of this form of cell death on key biochemical functions of the cell. Nonetheless, further modification of the fixing-staining methods presented here will be needed to make FACS useful for analysis of apoptosis in human cells.