Two strains of mice (Swiss and CF1), male and female, were used in this study. The mice drank either distilled water or 0.1% ascorbic acid in distilled water for one week prior to and during the experiments. Mice were irradiated in groups of 10; they received total body X-irradiation in a single exposure ranging from 200 R to 750 R. Time of death was recorded daily while weight changes and volume of water consumed were recorded every other day. At the low exposure levels, our results indicated that: a) mice drinking ascorbic acid in distilled water died about one week earlier than those drinking distilled water only, and b) the LD 50/30 was higher in mice drinking only distilled water. The differences between both groups were noticeable at exposures up to 550 R; at higher exposures, there was no difference. This study showed that high levels of ascorbic acid potentiated the effect of X-ray whole body irradiation.