The long term prognostic significance of oestrogen receptors was assessed in a prospective study of 767 patients presenting between the years 1975 and 1981 with stage 1 and 2 breast cancer treated by mastectomy with either full axillary dissection or nodal sampling. Oestrogen receptor binding was determined by a dextran coated charcoal method and median follow up was 11 years. Oestrogen receptors were present in 396 (54%) of tumours. Absence of oestrogen receptors was associated with tumours of high histological grade, but there was no relationship between nodal status or tumour size. Oestrogen receptor status did not predict survival for the group as a whole or when stratified by nodal status. In multivariate analysis both nodal status and tumour size were powerful independent prognostic factors, but oestrogen receptors failed to achieve statistical significance.