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).