Estrogen receptor (ER) is a member of the steroid-receptor family. Unlike protein growth factors that bind to receptors on the cell surface and activate signal-transduction cascades to influence gene expression, the steroid hormones bind to intracellular receptors, which then bind to DNA and regulate gene expression directly. ER-b has a molecular mass of approximately 53kD and is composed of six regions, A to F, on the basis of different amino acid sequence homology (2). The A/B region contains a transcription activation function. Region C encodes the DNA binding domain. Region D is involved in binding to hsp90, as well as containing nuclear localization signals and plays a part in stabilizing DNA binding by the DNA binding domain. Region E contains the hormone/ligand binding domain as well as hormone-inducible transcription activation function. Region F appears to play a role in modulating transcriptional activation by ER-a. ER-b was discovered in 1996 in rat prostate, as well as in secretory epithelial cells of the prostate and granulose cells of the ovary (1). Later, human ER-b was discovered and characterized and found to be expressed in human thymus, spleen, ovary and testis (3).