Variations in sensitivity of synchronized Chinese hamster cells to oxic and anoxic X-ray exposures

V-79 Chinese hamster cells in monolayer cultures on glass surfaces were synchronized by treatment with hydroxyurea and exposed at different times thereafter to X-rays in the air or in oxygen-free argon. Survival determinations indicated that the oxygen enhancement ratio OER as expressed by the ratio of the respective D0 values varied over a narrow range in the different phases of the cell cycle. These changes resulted from cyclic alterations in both aerobic and anaerobic D0 values, and perhaps in n values.