1) This experiment was carried out to study the combined therapy of anti-tumor agent with surgical operation, especially for the analysis of its administration period. The ascites hepatomas MH 134 was subcutaneously transplanted to the mice, C(3)H/HeN (♂) X dd (♀): F(1) hybrids, and nitromin was administered. 2) According to the survival rate in cases of the combined therapy of the agent with radical surgical operation, the preoperative administration appeared to be more effective than the postoperative. The survival rate is higher in the group with preoperative administration. 3) Death coused directly by tumor growth occurred in most of the cases within 90 days after tumor transplantation. There was hardly found any difference between the pre- and postoperative administrations. 4) The combined therapy seems to be apparent to increase the survival rate, compared with the non-treated group. 5) Some animals have metastases in lymphnodes, lung, liver and other organs without local recurrence in the group with postoperative combined therapy, while in that with preoperative combined therapy there was never seen a mode of such metastasis, but both of the local recurrence as well as metastases to those organs were observed. It seems to be due to the tumor cells in circulating blood at the time of surgical manipulation. It is therefore apparent that the preoperatively administered anti-tumor agent can inhibit the metastasis formation but the postoperative cannot.