Estrogenic activities of more than 90 chemicals including food additives, foodstuffs of plant origin, and some chemicals, which could be orally ingested, were examined by assaying estrogen receptor (ER)-dependent proliferation of MCF-7 cells. Among 66 food additives, 17 compounds stimulated the proliferation, but their concentrations giving maximal cell yield were higher than that of 17β-estradiol and their estrogenic activities were weak. Flavonoids had relatively strong estrogenic activities. In the assay of ER competitive binding to human ERα and ERβ in vitro, the antioxidant t-butylhydroxyanisole (BHA) had the capacity to compete with 17β-estradiol, while the capacity of o-phenyl phenol (OPP) was too small to calculate. Both BHA and OPP induced a decrease in gene expression of ERα and an increase in that of progesterone receptor in a time-dependent manner. These effects were similar to that of 17β-estradiol, a though much higher concentrations were required for these compounds than 17β-estradiol. These results may suggest that we should be careful not to ingest excessive food additives.