On the basis of the previous study, on the cell interaction between malignant tumor cells and other cells, especially with lymphocytes, the present study was carried out by investigating cell to cell interaction of human malignant tumor cells and human lymphoblastoid cells such as T-cell (MOLT-4 cell) and B-cell (Burkitt lymphoma cell). As a result it has been revealed that live lymphoblastoid cells were not adhered on the cell surface of the tumor cells, nor is it ingested by tumor cells, but in thepresence of HVJ (Sendai virus: 2,000 H.A. units) it adheres slightly on the cell surface of tumor cell but no cell fusion of tumor cells and lymphoblastoid cells is observable. On the other hand, the tumor cell as well as T-cell and B-cell all have receptors to concanavalin A (Con. A) on their cell surfaces, and they show a marked cell binding such as tumor cell and T-cell, tumor cell and B-cell, and there can be observed a marked phagocytosis of lymphoblastoid cells by tumor cells. Moreover, the tumor cells that have phagocytized lymphoblastoid cells undergo a marked cell destruction within 4 hours of cell-binding and phagocytosis, which is especially prominent in the case of phagocytosis of E.B cell by tumor cell.