Abstract: Objective To study the effects of benzene and the benzene metabolite hydroquinone on the cell cycle and apoptosis of peripheral blood lymphocytes,and to explore the molecular mechanisms underlying benzene-induced cytoxicity damage.Methods Human lymphatic cells were isolated,cultivated and then divided into three groups including of low,moderate,and high benzene exposure(0.25,3.5,50 μmol/L) and three groups of low,moderate,and high hydroquinone exposure(50,150,450 μmol/L).One solvent control and one blank control group were also set up.After the treatment,we assayed the growth arrest of lymphocytes induced by benzene and hydroquinone by methyl thiazolyl tetrazolium(MTT) test.Flowcytometry was applied to detect cell cycle and apoptosis rate.2,7-dichlorodihydro fluorescein diacetate(DCFH-DA) assay was used to detect reactive oxygen species(ROS) contents.Lymphocytes'DNA fragment was detected with single cell gel electrophoresis technology.Results The results showed that both benzene and hydroquinone decreased cell viability in a dose dependent manner,along with induction of S phase and G2/M phase arrest and increased late apoptosis.Meanwhile,benzene and hydroquinone induced accumulation of intracellular ROS in a dose-effect relationship.All data showed significant difference compared to control groups(P < 0.05).The mean tail lengths were 26.45±7.96 and 30.28±6.07 μm for groups of high levels of benzene and hydroquinone.The results revealed a significantly higher level of DNA damage in all concentration groups compared to control groups with a dose-effect relationship.Conclusion Benzene and its' metabolite hydroquinone could induce decreased lymphocytes viability,dysfunction of cell cycle and programmed cell death.The results indicate that the overproduction of ROS and DNA lesion are likely to contribute to benzene-induced cytogenetic changes.