We have treated 2 cases of simultaneous bilateral breast cancer by intra-arterial infusion chemotherapy (IA) and transcatheter arterial chemo-embolization (TAC-E), respectively. In the former case treated by I. A., both the treated tumor and the contralateral mass were remarkably regressed and necrotized. However, serious systemic side effects due to the intraarterially infused drug were observed. In the latter case treated by TAC-E, chemo-embolic effects were selectively observed in the treated tumor, and side effects were slight. On the other hand, a non-treated mass showed no changes. From these findings, we concluded that I. A. serves as a semisystemic therapy, and that TAC-E, at least in our subjects, works as a loco-regional cancer chemotherapy.