As a link in the studies of changes in the cancer progress and concomitant immunity in cancer-bearing body, we conducted a series of in vitro tissue cultures using JTC-11 cells (a cell line established from Ehrlich cancer cell) mixed with lymphocytes prepared from regional axillary lymph nodes, distant mesenterial lymph nodes, and spleen with lapse of time, from the DD mice previously transplanted with 500×10(4) cells/mouse of Ehrlich ascites tumor cells on the back under skin, and observed changes in the antitumor activity of these lymphocytes. As a result it has been demonstrated that by 5 days after Ehrlich cancer transplantation antitumor activity can be detected in any of lymphatic tissues, while by about 8-10 days there appears a strong antitumor activity first in the regional axillary lymph-nodes cells and lymphoid cells of spleen, but at this stage such an antitumor activity cannot yet be seen in the distant mesenterial lymph-node cells. After lapse of 15, 20 and 22 days a strong antitumor activity appears in the distant mesenterial lymph-node cells, which becomes stronger with lapes of time. On the other hand, in the spleen the antitumor activity weakens and disappears with lapse of 15, 20, and 22 days. In the case of axillary lymph nodes by 15th day there can still be observed a strong antitumor activity, which grows gradually weaker by 20th and 22nd days. The fact that, when left standing without any treatment, concomitant immunity in the cancer-bearing mouse destined to die of tumor death appears first in regional lymph nodes, which is gradually strengthened, and such a concomitant immunity appears later in distant lymph nodes, indicates that the concomitant immunity differs according to different sites of the body.