We have investigated the change of balance between proliferating and apoptotic tumor cells in dimethylebenz(a)-anthracene (DMBA)-induced rat mammary tumors by using anti-angiogenic drug, AGM-1470 and anticancer drug, 5'-deoxy-5-fluorouridine (5'-DFUR). The rate of PCNA positive proliferating cells was decreased in the tretment groups, especially in AGM-1470 and in the combination of AGM-1470 and 5'-DFUR. And apoptotic index evaluated by TUNEL method was increased in 5'-DFUR and in the combination group. The ratio of proliferating cells/apoptotic cells was markedly decreased in AGM-1470 and AGM+5'-DFUR group compared to control group. These data suggested that anti-angiogenic drugs might regulate the growth behavior of tumor cells by changing the microenvironments.