Damiana (Turnera diffusa Willd. Ex Schult) has traditionally been used as an herbal aphrodisiac. The study was aimed to investigate the anti-aromatse activity and the estrogenic activity of the constituents isolated from Turnera diffusa. The methanolic extract and 24 compounds isolated from the leaves of Turnera diffusa were evaluated for aromatase activity by using a tritiated-water release assay and for estrogenic activity by using yeast estrogen screen (YES) assay. The methanolic extract demonstrated a dose-dependent inhibitory activity of the aromatase enzyme with the IC(50) value of 63.1 microg/ml. Among the 24 tested compounds, pinocembrin and acacetin showed the most potent inhibition with IC(50) values of 10.8 and 18.7 microM, respectively. Estrogenic activity was also observed in the extract and three compounds including apigenin 7-glucoside, Z-echinacin and pinocembrin with EC(50) values of 10, 20 and 67 microuM, respectively. The extract of Turnera diffusa and two isolated compounds pinocembrin and acacetin could significantly suppress aromatase activity. Moreover, apigenin 7-glucoside, Z-echinacin and pinocembrin showed estrogenic activity.