Cancer claims the lives of more than six million people each year in the world. About 1,268,000 new cancer cases, and 553,400 deaths were reported in the United States in 2001. Current treatment approaches have yielded significant progress in the fight against cancer, but the incidence of developing certain types of cancer continues to rise. This is especially true in the African-American communities. African Americans are about 33% more likely to die of cancer than are whites and more than twice likely to die of cancer as are Asian-Islander, American-Indians, and Hispanics. This increase coupled with the harsh side effects of some of the cancer chemotherapies have led to the search for more natural biological products, especially those derived from plant products, currently known as herbal medicine. There is a need for a continued search for novel natural products that may be used as cancer chemopreventive and/or chemotherapeutic agents. The objective of this study was to evaluate the effect(s) of a novel water-soluble leaf extract of Vernonia amygdalina (VA) on human breast cancer cell DNA synthesis. MCF-7 cell line, considered a suitable model, was used in this study. Treatment of cells with physiologically relevant concentrations of water-soluble VA extract potently inhibited DNA synthesis in a concentration-dependent fashion both in the absence and presence of serum. Fractions of VA extract separated using preparative reverse-phase chromatography also inhibited DNA synthesis (P < 0.005). These results suggest that VA vegetable, if incorporated in the diet, may prevent or delay the on-set of breast cancer.