It has been proposed that intense immunohistochemical staining using the monoclonal antibody NCRC 11 is indicative of a better prognosis in breast cancer, and that expression of pregnancy specific glycoprotein (SP1) and epidermal growth factor receptors (EGFR) are poor prognosis indicators. In order to evaluate the significance of staining for NCRC 11 to prognosis and to these other variables, we studied two series of breast cancer patients. In one series (n = 93), staining with NCRC 11 and for SP1 was correlated with prognosis: in neither case was there any overall relationship between staining and survival. However, when the patients were stratified by tumour histological (Bloom's) grade, SP1 expression was associated with a poorer prognosis in grade II tumours (p less than 0.025). In a further series (n = 94), NCRC 11 staining was carried out and fresh tumour samples were assayed biochemically for oestrogen receptor (OER) and EGFR. NCRC 11 showed a negative correlation with EGFR status (p = less than 0.05) but no significant association with OER status. Thus despite our demonstration of a negative correlation with an indicator of poorer prognosis, we were unable to demonstrate any direct relationship between staining with NCRC 11 and survival.