Modulation of the immune response to allogenic and syngeneic cells and conventional antigens by immunopotentiators will be examined in the experimental program proposed. Emphasis will be placed in defining conditions under which Bacillus Calmette-Guerin (BCG) and MER (a methanol-extraction residue of BCG) stimulate and suppress the ability of the host lymphoid cells to respond to allogeneic and syngeneic tumor cells as measured in in vitro cytotoxicity assays, and the cellular basis for these effects. A comparison will be made of the "suppressor cells" (macrophages?) induced by BCG and those macrophages cytotoxic for tumor cells in vitro. In addition the structural requirements for B cell triggering will be further investigated using lipopolysaccharide (LPS) and its chemically modified derivatives. Since the use of immuno-potentiators clinically in treatment of some forms of cancer is currently being evaluated, continued investigation of the biological basis of their mode of action should aid in an understanding of the scope of their usefulness and limitations.