In 23 cases of primary advanced breast cancer, intra-arterial infusion chemotherapy of Adriamycin (ADR) and Mitomycin C (MMC), which were injected jointly or individually, was performed and its effects and side effects were studied. As for the clinical effects, the response rate (CR + PR) was 73.9% (17/23 cases) and the histological response rate (greater than grade IIb) was 82.6% (19/23 cases). ADR alone (100-150 mg) and MMC (28 mg) + ADR (42 mg) combined regimens were especially superior in both their clinical and histological effects. In metastatic lymph nodes, the histological response rate was 78.9% (15/19 cases). As for the side effects, in the cases treated with MMC, bone marrow suppression such as leukocytopenia and thrombocytopenia was remarkable and took a long time to recover. The above results suggested that the most effective regimen for primary advanced breast cancer using intra-arterial infusion chemotherapy is ADR alone, in single doses of 50 mg up to a total dose of 150-200 mg. Histological examination of the effective cases revealed that the central region of the tumor was more markedly recrotic than the periphery. It was suggested that the grade of the effects on tumor tissues is related to the mechanism of anticancer agents.