In peplomycin-supersensitive Chinese hamster lung cells, the increase in poly(ADP-ribose) synthesizing activity following peplomycin treatment was significantly reduced as compared with the parental lung cells, suggesting that peplomycin-supersensitive lung cells may have some deficiency in DNA repair. On the contrary, peplomycin-supersensitive ovary cells, which undergo increased DNA damage induced by peplomycin, showed normally increased poly(ADP-ribose) polymerizing activity compared with the parental ovary cells. Relationship between poly(ADP-ribose) polymerase and peplomycin sensitivity was discussed.