Oestrogen receptor (ER) content was measured in 257 patients presenting with 'operable' breast cancer. Difference in age, menopausal status, parity, age at first pregnancy, breast feeding habit and details of past and family history were compared with oestrogen receptor status. The symptoms and their duration together with the extent of the disease both clinically and pathologically were also compared with receptor status. Association both for increasing age and postmenopausal status was found when oestrogen receptors were present in the primary tumours in significant quantities. No separation between the effect of age and menopausal status on oestrogen receptor status could be distinguished. No relationship was demonstrated between oestrogen receptor status and the other clinical and pathological factors examined.