Cellular sensitivity of AA8 and UV41 to hydrogen peroxide (H2O2), bleomycin and paraquat was investigated by clonogenic survival assays. Both XPF-defective UV41 and ERCC1-defective UV20 showed sensitivity to H2O2. UV41 corrected by the human XPF gene showed a similar resistance to H2O2, compared to AA8. UV41 cells also displayed sensitivity to bleomycin and paraquat. Closed circle, AA8; opened circle, UV41; open triangle, UV20; open square, UV41 expressing XPF. The bars indicate standard deviations obtained from three independent experiments. Single asterisks and two asterisks indicate the results of the Student’s t-test, P<0.01 and P<0.05, respectively. The difference in the survival between AA8 and UV41 at 100 µM bleomycin treatment was not statistically significant. The actual values for each concentration in the graphs are summarized in Table S-1.