In 101 mice, Lewis lung tumor (25 mg apiece) was implanted subcutaneously in the right hind limb and the mice separated into various groups and protocols to test treatment with immunotherapeutic and chemotherapeutic agents. In those treated intralesionally with BCG, the growth of primary tumor was retarded (P ≤.05). Tumor growth in animals treated with systemic BCG and serum from tumor-bearing mice was not different from controls. In 14 of 20 mice treated with chemotherapy (semustine and cyclophosphamide), there was no primary or metastatic growth (P ≤.01). The observations show that this sort of systemic immunotherapy had no effect on mouse Lewis lung tumor, that intralesionally there was a retarding effect of BCG (although it did not influence metastases), and that this protocol of chemotherapy was strikingly effective.