Five peptides, corresponding to regions of the predicted protein sequence of the oestrogen‐regulated pNR‐2 protein which is expressed in oestrogen‐responsive human breast cancer cells, were synthesized. Two peptides were immunogenic in rabbits and antisera against one peptide reacted with the pNR‐2 protein in sections of formalin‐fixed, paraffin‐embedded breast tumour. There was a significant correlation between the extent of pNR‐2 protein expression detected by immunohistochemistry and pNR‐2 mRNA levels determined by hybridization with a cDNA probe in a series of primary breast tumours. pNR‐2 expression was assessed immunohistochemically in a panel of normal tissues. Expression was detected in normal breast, small intestine, and stomach (body and antrum).