Immunization of CC57Br mice with irradiated Krebs-2 carcinoma cells renders no influence on the rate of ascites aggravation in subsequent transplantation of the tumor but increases considerably life-terms of tumor-bearing animals. Immunization with tumor cells in combination with not high doses of BCG results in a reverse development of ascites in some mice and a complete disappearance of tumor in them. With increased dosage of the vaccine the number of animals with ascites regression is increased, but their life-terms are reduced due to reactivation of the tumor process and, presumably, to the development of autoimmune lesions.