A series of 193 archival breast cancer biopsies were analysed immunohistochemically to detect over-expression of c-erbB-2 oncoprotein. Altogether, 59/193 (31%) of the tumours were positive for c-erbB-2, the staining being located at the cell membranes with weak cytoplasmic staining in some samples. The expression of c-erbB-2 was positively correlated with a number of parameters analysed: ductal type, intraductal growth pattern, high tumour grade, density of tumour infiltrating lymphocytes (TIL), DNA aneuploidy, steroid (ER, PR) receptor negativity, high S-phase fraction, high mitotic frequency, high values of nuclear factors, and accumulation of p53 protein. c-erbB-2 expression showed a weak association with a low survival probability (p = 0.07) and with a short recurrence-free survival (p = 0.1). In local tumours or in axillary lymph node positive tumours, c-erB-2 expression had no significant prognostic value. Also in multivariate analysis, c-erbB-2 expression had no independent prognostic value superior to the axillary lymph node status, tumour diameter and mitotic frequency. The results show that c-erbB-2 expression in related to several histopathological features of malignancy and cell proliferation in breast cancer, but it has no independent prognostic value better than that of the established prognostic factors.