Genistein is an isoflavonoid phytoestrogenic compound found in soybeans, pea pods, and other legumes. The estimated human normal dietary intake of genistein, primarily as glycosides, is 0 to 0.5 mg/kg. Genistein is present in much greater amounts in nutritional supplements. Genistein is carcinogenic in female neonatal mice, inducing endocrine-dependent uterine tumors in a fashion similar to diethylstilbestrol (DES). Genistein is a tyrosine-specific inhibitor of protein kinase activity, blocking the tyrosine-phosphorylation of histone H2B. In adult animals, dietary genistein has chemopreventive effects on breast, prostate, and other endocrine-dependent tumors.