This study evaluated the estrogenic and antiestrogenic activities of native and in vitro hepatic metabolized tuberous extracts of wild Butea superba collected from 23 out of the 76 provinces in Thailand by yeast estrogen screening (YES). The YES screen used consisted of the human estrogen receptors hERα and hERβ and the human transcriptional intermediary factor 2 or human steroid receptor coactivator 1, respectively, together with the β-galactosidase expression cassette as the reporter. The relative potency, effectiveness and relative inductive efficiency were evaluated by determining the β-galactosidase activity (EC(50)) of each tuberous extract in relation to that induced by 17β-estradiol. Six pure compounds isolated from B. superba were tested in parallel and exhibited a maximum relative potency compared to 17β-estradiol of 15.5% and 5.27% in the respective hERα and hERβ assays. Eighteen and seventeen plant extracts were respectively found to interact with the hERα and hERβ receptors in the YES assays with higher relative potency and relative inductive efficiency with hERβ than with hERα. The selected plant extracts tested exhibited antiestrogenic activity. Coincubation with the rat liver S9 mixture also elevated the estrogenic potency of these plant extracts.