To search for possible untoward effects of surgical manipulation of a malignant tumor, a series of experiments was carried out using VX2 carcinoma of rabbits. Fourteen days after inoculation of VX2 carcinoma into the liver, the rabbits were separated into two groups: Group I, manual manipulation during relaparotomy; and Group II, relaparotomy alone without manual manipulation of the tumor. After these procedures, the tumor was surgically removed and histologic examinations were made. The incidence of vascular permeation of liver tumor cells into the hepatic vein was significantly higher in Group I (P less than 0.01). On the 14th day after resection of the tumor, the number of metastatic nodules in the lungs was significantly increased in Group I (P less than 0.01). Survival time of rabbits after resection of tumor was significantly shorter in Group I (P less than 0.01). These results are taken to mean that manual manipulation of a tumor may well enhance metastasis.