The chemical and nutritional composition of dry beans varies among market classes. Previous reports have shown that beans differ in their ability to accumulate micronutrients and in their content of phytochemicals that have been linked to positive health benefits.  Scientists have attributed the health benefits of beans, e.g. anti-cancer effects, to their high concentrations of folate and fiber, as well as to lower the glycemic index.  The objective of this program of research is to characterize 13 different market classes of dry beans (Phaseolus vulgaris L.) for their health benefits based on chemical assays, and in-vivo activity using laboratory animals. Our results confirm that market classes differ in phenolic content, antioxidant activity, and biological activity in laboratory animals. In general, white beans were classified low and colored beans intermediate or high for antioxidants and phenols. Results from animal feeding trials confirmed that market classes differed for their cancer preventative activity and pink, red, and black beans had the highest reduction of mammary pathologies. There is evidence that beans from Central America or Mexico have greater protective capacity than beans from Andean South America. These results will lead to insight into which beans have the greatest potential to alter human disease and provide plant breeders with information that will allow them the opportunity to improve the nutritional value of dry beans.