We have analysed the expression of bcl-2 protein retrospectively in 34 primary male breast carcinomas (MBC), using the monoclonal antibody bcl-2 in formalin-fixed, paraffin-embedded tissues. Bcl-2 expression was compared with tumour clinicopathological features, sex steroid hormone receptors, DNA content, p53 immunoreactivity and cell proliferative activity assessed by counts of the argyrophilic nucleolar organizer regions (AgNORs), the monoclonal antibody PC10 against proliferating cell nuclear antigen and the monoclonal antibody MIB-1. Most (28, or 82.3%) of the 34 cases of MBC were bcl-2 positive. No association was found with clinicopathological features of the tumours, although bcl-2 tended to be more frequently expressed in small tumours (P=0.09) and in cases without necrotic areas (P=0.1). Nor was any association found with hormone receptor status, p53 immunoreactivity, DNA content, cell proliferative activity or patient survival. In multivariate analysis, only proliferative activity (expressed by AgNOR counts) and p53 immunoreactivity had independent prognostic significance. Our results indicate that MBC differs from FBC in that in MBC bcl-2 protein is not related to an oestrogen-dependent transcription pathway and bcl-2 alone is not sufficient to induce increased proliferation. These characteristics, together with the high prognostic value of cell proliferation and the lack of prognostic significance for hormone receptor status, support the hypothesis that MBC is biologically different from FBC.