Swiss mice drank either distilled water or 0.1% ascorbic acid in distilled water for one week prior to and during the experiments. Solid tumors were induced by injecting Ehrlich ascites tumor cells i.m. into the hind limb of Swiss male and female mice. It was found that the tumor growth was significantly faster in the mice that were drinking distilled water. Beginning two days after tumor cell injection, the tumor bearing limbs were irradiated every 24 h as follows: a) 6 exposures of 400 R, 500 R, 600 R, or 700 R each, b) 10 exposures of 400 R each, and c) 11 exposures of 400 R each. Our results indicated that when 6 exposures of 700 R each were given every 24 h to mice drinking distilled water, about 80-85% tumor control was achieved; the percent tumor cure was even better in mice drinking ascorbic acid in water than in mice drinking water.