The effect of 32 flavonoids on androgen (AR) and glucocorticoid receptors (GR) was investigated using an MDA-kb2 human breast cancer cell line to predict potential AR and GR activities. Among them, 5-hydroxyflavone (7) had the highest AR antagonistic activity with an IC(50) value of 0.3 microM, whereas 6-methoxyflavone (11) had the highest induced luciferase activity with an EC(150) value of 0.7 microM. Genistein (2) and daizein (1) showed a sufficient increase of luciferase activities as their concentrations increased with EC(150) values of 4.4 and 10.1 microM, respectively. These findings provide evidence of a fundamental property of their structure-activity relationship with AR and/or GR.