Objective:To study the effects of low concentration of ar senic (As 2O 3) on DNA synthesis and related transcription factor gene E2F1 express ion in keratinocyte. Methods:Human epidermal keratinocyte (cell line HaCaT) cultured in vitro was used. After treatment with various concentrations of arsenic, DNA s ynthesis and E2F1 expression in HaCaT cells were detected by using 3H-TdR method and RT-PCR.Results:Arsenic caused a modest increase of keratinocyte DNA synth esis when the concentration reached the range within 0.5-16 nmol/L, but the amo unt of incorporated 3H-TdR decreased and returned to baseline level when th e concentration of arsenic increased to over 16 nmol/L. RT-PCR analysis showe d the level of E2F1 mRNA was elevated in HaCaT cells with the increase of DNA sy nthesis. Conclusion:Arsenic of a certain concentration could increase DNA s ynthesis and enhance E2F1 expression in HaCaT cell line, which might be one of t he pathological mechanisms of skin disease related to arsenic. Objective: To study the effects of low concentration of ar senic (As 2 O 3) on DNA synthesis and related transcription factor gene E2F1 express ion in keratinocyte. Methods: Human epidermal keratinocyte (cell line HaCaT) cultured in vitro was used. After treatment with various concentrations of arsenic, DNA synthesis and E2F1 expression in HaCaT cells were detected by using 3H-TdR method and RT-PCR. Results: Arsenic caused a modest increase of keratinocyte DNA synth esis when the concentration reached the range within 0.5-16 nmol / L, but the amo unt of incorporated 3H-TdR decreased and returned to baseline level when th concentration of arsenic increased to over 16 nmol / L. RT-PCR analysis showe d the level of E2F1 mRNA was elevated in HaCaT cells with the increase of DNA sy nthesis. Conclusion: Arsenic of a certain concentration could increase DNA synthesis and enhance E2F1 expression in HaCaT cell line, which might be one of t he pathological mechanisms of skin disease relate d to arsenic.