1) This study was made to find out the possibility of metastasis of tumor cells via circulating blood and also the effect of anti-tumor agent to the cells transfered through blood. Nitromin was used as an agont. The blood of the C(3)H/HeN (♂) X dd (♀): F(1) mice subcutaneously bearing ascites hepatomas MH 134 was subcutaneously given to the tail of another group of intact F(1) mice. 2) The metastasis was appeared to be possible without any relation of the time interval between the tumor transplantation to the donors and the blood injection from the donors to the recipients. Transplantation was not successful when the anti-tumor agent was given within the interval. 3) The survival time seems to be kept constant in cases of successful transplantation. 4) Transplantation was more successful from cases bearing large tumors and surviving for longer periods, and from cases bearing small tumor and surviving for shorter period. 5) The same is true in weight of the tumors. 6) The spleen of the tumor-bearing mice weighed more than that of the non-bearing mice. The group treated with chemotherapy tends to have less weighing spleen in contrast to the non-treated group. It is interesting to note that the tumor-bearing mice whose blood could form metastasis in another mouse appeared to have the heaviest spleen.