The expression of oestrogen (ER), progesterone (PR) and androgen (AR) receptors in female breast cancer was investigated by immunohistochemistry on snap-frozen tissue specimens of a series of 100 breast cancers. For detection of the AR we used a recently developed mouse monoclonal antibody specific for the N-terminal domain of the human AR. Expression of AR was compared with that of ER and PR as well as with tumour grade and age. Of the breast cancers investigated, 76% were AR-positive. This high percentage corresponds well with previous data on AR expression in breast cancer determined with ligand-binding assays. In 53% of the tumours AR, ER and PR were present, while 9% of the tumours were positive for AR and negative for ER and PR. In 13% of the tumours no ER, PR or AR expression was seen; these were all grade-III tumours. A positive correlation was found between age and ER expression, but no correlation was seen between age and PR or AR. Future studies should establish the prognostic value of the combination ER, PR and AR determinations on female breast cancer with regard to biological behaviour and response rate to hormonal therapy.