Hoechst 33342 is a kind of fluorescent dye used for evaluating the cell cycle and apoptosis in a variety of benign and malignant cell lines,such as BC3H-1 monocytes,HI-60 cells,HT-144 melanoma cells and hepatoma cells.The inhibitor of topoisomerase I,the alternation of TATA box binding protein.the intraeellular accumulation of E2F-l protein and the mitochondrial dysfunction may play an important roles in the apoptosis pathway indueed bv Hoechst 33342.