The immuno-modulating effect of three immunopotentiators (OK-432, PS-K, Levamisole) was studied in MH-134 bearing C3H/He mice using foot pad reaction. When tumor bearing mice were injected their own tumor cells in foot pad, foot pad thickning was observed. Microscopic examination revealed that this thickning was not due to tumor growth but caused by polymorphonuclear and mononuclear cell infiltrations. This reaction was specific to their own tumor cells and was able to be transfered by spleen cells and peritoneal exudate cells. Immunopotentiators, when administered prior to tumor inoculation, these three agents had no effects on foot pad reaction, but when administered after tumor inoculation PS-K enhanced the foot pad reaction. Although cyclophosphamide had a significant suppressive effects on foot pad reaction, the reaction was restored by the concomitant use of these three immunopotentiators. This findings suggested that these immunopotentiators might restore the patient's immunity against one's own tumor when used concomitantly with cytotoxic agents in the management of cancer patient. On the other hand, concomitant use of carragheenan with OK-432 or Levamisole resulted in enhancing the suppressive effect cauced by carragheenan alone.