SummaryThe incidence of susceptibility of inbred mice to 2 transplantable neoplasms, L1210 leukemia and adenocarcinoma 755, was not influenced by variation in the dietary fats. Diets deficient in fat likewise had neither inhibiting nor stimulating activity in the pathogenesis of the 2 neoplasms.The authors are indebted to Dr. Clyde Culbertson and Dr. Irving Johnson, Eli Lilly and Co., for help in supplying mice and transplantable tumers, and to Mr. James F. Glore, Dept. of Illustration at the Medical Center, for preparation of graphs. The capable technical assistance of Pearl Driver, Betty Corya, Shirley Stockslager, and Donna King is also appreciated.