[Cancer and BCG].

In the present paper the modification that BCG induces on experimental tumor growth and its possible human medical applications are analyzed. The mechanisms by which the BCG inoculated mixed with tumor cells enhance its rejection involve the participation of different cell populations, such as sensitized lymphocytes, activated macrophages and the spontaneous cytotoxicity effector cells (N. K. cells). The tumor rejection depends on the BCG doses and the inoculation modes. In this regard, high doses induce toxic effects and can activate suppressor mechanisms mediated by cells or serum factors. The action of BCG on tumoral growth is apparent only under certain circumstances where the host-tumor system should be carefully selected.