Certain chemotherapeutic agents against cancer have been used clinically as an immunosuppressive drug. In recent immunological advances it has been demonstrated that some chemotherapeutic agents can modify the antibody production and delayed-type hypersensitivity. In connection with modification of anticancer immune responses by the agents, many investigators have reported the increased production of NK cells in normal animals and of effector T cells in tumor-bearing animals, after administration of agents. Some authors have emphasized the possible role of the agent given before the tumor-inoculation for enhancement of host-mediated anti-tumor response on subsequent tumor growth. In general, these beneficial effects associated with the agents have been attributed to the abrogation of either suppressor T cells or macrophages. On the other hand, some reports including recent ones from this laboratory have described the production of tumoricidal macrophages by i.p. injection of the agent. The underlying mechanism (s), though not yet apparent, seems to be related to activation of macrophages. A small body of clinical suggests evidence suggesting immunoaugmentation by chemotherapy, but the therapeutic significance remains obscure. Though the immunoresponses , response components and the agents examined are heterogeneous and some results are restricted in a special experimental model, the immune response increase by anticancer chemotherapeutic agent in generally conceivable, and it should be further studied from the viewpoint of the host-mediated therapeutic effect.