Experiments are reported showing some slight protective capacity of guinea pig antimouse leukemic tissue serum to protect the AKR mouse against the BW5147 tumor, when the serum is first adsorbed to remove precipitating antibody for the tissue cell antigens. The degree of protection is slight, and all mice eventually died of the tumor development. Results of one injection of tumor tissue – oleic acid emulsion show up to 46% survival of the immunized mice following challenge injections of active tumor preparation. No protection is seen after a similar injection of tumor material which had remained frozen for several months. Repeated injection of frozen tumor tissue produced leukemic tumor development in test mice, indicating that this material retains some activity under these conditions, and that sufficient immunity cannot be produced by these injections to protect against the disease.