Epidermal growth factor (EGF) is a potent mitogen for many tissues including breast. The receptor for EGF (EGF-r) has the same peptide sequence as a known oncogene. Sixty-one human breast cancers and nine associated lymph node metastases have been examined for the presence of EGF receptors by competitive binding and immunocytochemical techniques. Oestrogen receptor analysis on the same specimens was performed by the dextran coated charcoal method and compared with EGF-r status. These were correlated with the clinical findings and histological data. An inverse relationship between EGF-r and ER was found (chi 2= 7.81, P less than 0.01) with a higher incidence of EGF-r positive tumours in the metastatic group (chi 2 = 14.51, P less than 0.001). EGF-r positive tumours were of poor differentiation and had characteristics associated with poor prognosis.