With the recent advances in the immunological surveillance system, an understanding of the role of host immunity has become essential to the management of carcinogenesis, tumor proliferation, recurrence and metastasis. Although it is important to continue chemical and surgical treatment of cancer, support of the anti-tumor immune system of the host should also be considered. Long term remission has been reported in leukemia by treating with BCG after chemotherapy whereas surgical treatment is usually more effective in preventing cancer recurrence in digestive organ cancer. The first step is extirpating the tumor as thoroughly as possible and the second step is chemo-immunotherapy. Cancer immunity, however weak, constitutes the basis for other treatments in selectively attacking cancer cells remaining after surgery, chemotherapy or irradiation. Immunotherapy should thus not replace chemotherapy or radiotherapy, but these methods should be employed in combination to attain more favorable results.