We report the effects of Antineoplaston A-10 Injection on the growth curve of human breast cancer (R-27) serially transplanted to athymic mice. The intraperitoneal administration of 1/4 LD-50 (50 mg/mouse) of Antineoplaston A-10 Injection every day and 1/2 LD-50 (100 mg/mouse) every other day for 35 days was found to significantly inhibit the growth curve and also the 3H-TdR uptake was inhibited by 73.7% in those given 1/4 LD-50 and by 77.1% in those given 1/2 LD-50. The tumor histology in both groups showed necrosis but no lymphocyte infiltration.