Formerly, concerning the relation between hormone and heterotransplantation, the author reported that, while teststerone inhibited heterotransplantation, estrogen and testectomy acceralate it. In this experiment, mice of R(3) strain were used. All mice were transplanted of mammary carcinoma from the R(3) strain of female mouse. The conclusions of this experiment are as follows; 1) Testaterone inhibited the homotransplantation and growth of tumor. 2) Estrogen and testectomy acceraiate the homotransplantation and growth of tumor.