In this report, an effective way of B.C.G. in combination with splenectomy is presented for cancer therapy. Ehrlich ascites cancer was inoculated into the footpads of DDS mice. At the appropriate times of tumor growth, a femur was amputated to remove the primary tumor. After several days, the host was rechallenged with Ehrlich ascites cancer. The challange was considered as metastasis. For the first experiments, mice were injected with B.C.G. into primary inoculated tumor and also splenectomized at the amputation. The combined therapy of B.C.G. injection and splenectomy prolonged survival, whereas neither B.C.G. injection nor splenectomy alone did not. For the next examination, the influence of B.C.G. presensitization with or without splenectomy on survival was examined. It was confirmed that the combined therapy was useful for the prolongation of survival. Furthermore, when Ehrlich ascites cancer was reinoculated with sera obtained from tumor bearing mice, splenectomy effectively prolonged survival. The data suggest that B.C.G. therapy is effective for host survival, especially when splenectomy is also performed.