A recently developed and validated histochemical method--immunogold-streptavidin enhancement--was used to determine oestrogen receptor content in paraffin sections of breast cancers. The selection of the best cut-off point to define oestrogen receptor status as rich or poor was made on the basis of survival data, using the following indices: survival to term; disease-free interval; survival at 5 years; and disease-free interval at 5 years. Oestrogen receptor status was examined in relation to histological grade, lymph node status, menopausal status and tumour size and these four indices were considered as independent prognostic factors. Semi-quantitative assay of receptor content showed that increasing content was related to better prognosis. Adjuvant therapy alone had no effect on patient outcome. Independently, histological grade and lymph node status, but not menopausal status or tumour size, were prognostic indicators. Oestrogen receptor rich status, as measured by immunogold-streptavidin, in conjunction with certain of these factors indicated a better prognosis. This was comparable with results in reports using other methods of receptor assay. We found the oestrogen receptor status and menopausal status more significant at 5 years than at term. The advantage of immunogold-streptavidin enhancement, which we found as reliable as other methods for oestrogen receptor assay, is that it can be used on archival, routinely paraffin-processed material.