The pNR-2/pS2 protein is regulated by oestrogens in breast cancer cell lines. This report describes a systematic survey of pNR-2/pS2 expression in a number of common epithelial tumours. Expression was evaluated immunohistochemically in an archival series using antisera raised against the C-terminus of the pNR-2/pS2 protein. Expression of pNR-2/pS2 by malignant epithelial tumours was widespread. Intense immunohistochemical staining was found in tumour cells in a proportion of pancreatic (6/8), large intestinal (7/12), gastric (9/16) and endometrial (4/12) carcinomas. Positive staining for the pNR-2/pS2 protein was also found in both benign and malignant ovarian epithelial tumours and was very significantly associated with mucinous differentiation (P less than 0.00001). Small numbers of carcinomas of bladder (2/10) and prostate (2/7) showed less intense staining and single examples of cervical carcinoma (1/7) and lung carcinoma (1/19) stained positively. None of the renal carcinomas (0/16) examined stained positively. Positive staining showed no correlation with gender. Although there are reports of oestrogen receptor expression in most of the tumour types considered, the possibility of other regulatory influences must also be considered. The pNR-2/pS2 protein may well have a more general role in human epithelial neoplasia than hitherto realised.