Chemotactic response of macrophage to PHA was depressed at early stages in allogeneic sarcoma 180-bearing ICR mice and syngeneic X5563-bearing C3H/He mice and their depressed response were restored to the normal levels by PSK. Macrophages-dependent resistance against Listeria monocytogenes at early phase of infection was depressed at the early stage after tumor inoculation. The depressed resistance was restored by PSK in X5563-bearing mice and by a combination of tumor resection and PSK in sarcoma 180-bearing mice.