Analysis of lymphocytes-derived DNA comets in different groups. A, lymphocytes nuclei of control (non-smokers), active- and passive smokers were analyzed for DNA damage by comet assay. Control group has intact nuclei with no tail. In case of active smokers group, the comets of significant length were observed compared to control. Also, the nuclear damage was found in passive smoker group. However, it was less than active smoker group. B, quantitative analysis of TCS values among different groups of active and passive smokers compared to control group. A, B and C are the Duncan’s variables representing statistical significance among groups. Quantitative analysis showed a significant increase in DNA damage in active and passive smokers compared to control group (*p˂0.05).