We have previously demonstrated that specific antitumor cell-mediated immunity in host mice was induced or enhanced by local irradiation to tumor. In this study, the immunological status of host mice with transplanted tumor were modified by using OK-432 as immunostimulator and cyclophosphamide as suppressor of suppressor T-cells before and/or after local irradiation to tumor. The results indicate that the combined use of immunomodifier and radiation is more effective in the tumor radiotherapy. Three factors as follows: the interval of drug and radiation, the times of treatments and dose of immunostimulator and immunosuppressor, are very important in these combined therapy.