Experiments were performed to explore the influence of local chemoimmunotherapy by intratumoral administration of mitomycin C (MMC) and/or BCG on the survival rate, lymph-node metastasis, growth pattern of rechallenge tumor, and host immune function, using a host-tumor system consisting of C3H/He mice and syngeneic tumor MH134. Combined intratumoral regimens of MMC plus BCG yielded a significantly higher survival rate than those achieved with BCG or MMC alone. Furthermore, the incidence of metastatic involvement of regional lymph nodes was also remarkably reduced in the combined regimen group. The group given the combined MMC-BCG regimen also showed a marked suppression of the growth of rechallenge tumor after surgical removal of the primary tumor and showed a greater induction of tumor-specific immunity than that seen in the group given intratumoral BCG injection alone. Both the delayed-type hypersensitivity, as measured by the footpad swelling assay, and the antibody response in spleen lymphocytes, as estimated by the plaque-forming cell assay, were found to be substantially depressed following a systemic injection of MMC, whereas the intratumoral administration of MMC had little or no effect on these parameters.