The transplantable murine ascites tumors, P388 leukemia and Ehrlich carcinoma, demonstrated complete inhibition of mitotic activity after treatment with dehydroascorbic acid in mice. Citric acid at the same pH value (2.4), however, showed no diminution of mitoses. Microscopic examination of the stained ascites exudate taken from the mice treated with 10 mg dehydroascorbic acid revealed few tumor cells and a pronounced increase in white blood cells, whereas the ascites tumor exposed to citric acid appeared normal.