Context
The widely held believe that oestrogen receptor (ER) signalling is mediated via nuclear receptors is now being challenged with a resurgence of interest in a putative plasma membrane ER, first identified over 20 years ago (see Additional information). This has come about as a consequence of some of the very rapid effects of ER ligands which have been reported. The aim of this work was to identify the presence of plasma membrane ER in the human breast cancer cell line MCF-7 and to define its action.