In 135 primary breast cancers, there was a significant inverse relation between epidermal-growth-factor receptor (EGFR) and oestrogen receptor (ER) status, and a significant association with tumour size and poor differentiation. The relapse-free survival and overall survival were significantly worse for patients with EGFR+ tumours compared with EGFR- tumours. Relapse-free survival and overall survival were also worse for patients with ER- tumours compared with ER+ tumours. Of the 71 ER- patients 28 were EGFR+ and 43 were EGFR-. The relapse-free and overall survival for ER- but EGFR+ patients were significantly worse than for "double-negative" patients. Moreover, relapse-free survival and overall survival for "double-negative" patients were similar to those for ER+ patients. Thus EGFR status divides the ER- population into good and poor prognosis subgroups. The presence of EGFR was the most important variable in the primary tumours for predicting relapse-free and overall survival. Multivariate analysis showed that EGFR status was the most important variable in predicting relapse-free and overall survival in lymph-node-negative patients, and the second most important variable in lymph-node positive patients.