When a ligand binding or enzyme immunoassay is used, meningiomas are found to be rich in progestin receptors (PR) whereas oestrogen receptors (ER) are virtually undetectable. A protein that can bind to an oestrogen responsive element (ERE) was detected in meningiomas, by using the band-shift assay. The binding of ER to the ERE is inhibited by the anti-ER monoclonal antibody ER-P31, which is directed to the A/B domain of the ER, indicating that the binding protein is an ER-like protein.