The significance of epidermal growth factor receptor (EGFR) status as a prognostic indicator was investigated by a competitive binding assay in 135 primary breast cancer patients. 55 patients (41%) were EGFR positive and EGFR status was negatively correlated with oestrogen receptor (ER) status (P less than 0.01). 5-year postoperative follow-up showed that relapse-free survival for EGFR positive patients was significantly worse than that for EGFR negative patients (P less than 0.05). There was no difference between the two groups in tumour size, axillary node involvement, age and menopausal status. Analysis by axillary node status demonstrated the poor prognosis of the EGFR positive group in node positive patients. As yet, no difference in prognosis has been seen in node negative patients. A higher frequency of haematopoietic relapse was observed in EGFR positive patients. Simultaneous or sequential EGFR measurements in primary tumour and metastatic sites of 34 patients showed that expression of EGFR was more enhanced in metastatic sites.