The evaluation of the immunohistochemical expression of epidermal growth factor receptor (EGFR), c-erbB-2 oncoprotein, proliferating indices Ki-67, and PCNA were determined on 68 primary breast carcinomas. These markers were correlated with each other and with other clinicopathological variables such as: age, tumor size? histotype, tumor grade and steroid receptors' content as well as nodal status. The monoclonal antibodies anti-human Epidermal Growth Factor Receptor (EGFR1), anti-human Ki67 (DAKO) and N13259 (Oncogene Science) were applied to paraffin and frozen tissue sections. All markers showed an heterogeneous pattern of staining. There was almost equally high staining intensity at the membranus for EGFR and c-erbB-2 in about 32% of the cases. The EGFR and c-erbB-2 positive cases were much less common in infiltrating lobular (2,2/13) rather than in ductal adenocarcinomas (21,20/55). The low grade carcinomas showed low expression of EGFR and c-erbB-2 oncoprotehl comparing with high grade ductal adenocarcinomas. A high index of Ki-67 was correlated with EGFR and c-erbB-2 membrane positivity. There was an inverse relationship between the expression of c-erbB-2 and EGFR, when compared with oestrogen receptors' content. A significant correlation was also demonstrated between EGFR and c-erbB-2 immunoreactivity with lymph node status. Our results provide evidence that the synchronous immunohistochemical detection of EGFR, c-erbB-2 and Ki-67 may be of useful significance in breast cancer patients, especially when combined with other clinicopathological variables. Furthermore the expression of EGFR and c-erbB-2 oncoprotein may affect the cell proliferation and differentiation.