The c-erbB-2 gene codes for a membrane receptor protein that is homologous to the epidermal growth factor receptor. Differential polymerase chain reaction (PCR) is an alternative semi-quantitative method for evaluating gene amplification and can be performed in formalin-fixed paraffin-embedded specimens. We aimed to compare differential PCR and IHC (immunohistochemistry) in the determination of c-erbB-2 status of breast cancers. Correlation between the prognostic impact of c-erbB-2 gene amplification and protein overexpression with conventional prognostic factors were also evaluated. Differential PCR and IHC for c-erbB-2 were performed on formalin-fixed paraffin sections of 60 invasive breast cancers. Results and the relation with the other prognostic parameters were compared. A highly significant degree of concordance between differential PCR and IHC in the evaluation of c-erbB-2 status of breast carcinoma was detected. Amplification and overexpression were significantly related to the number of metastatic lymph nodes, histologic grade, and lymphatic invasion but not age, histologic type, tumor size and estrogen status. We demonstrated and confirmed the importance of c-erbB-2 overexpression and amplification as a single and combined prognostic parameter together with conventional factors and confirmed that it can be detected by both immunohistochemistry and differential PCR techniques in breast carcinoma. This semi-quantitative technique provides reliable results and can be used routinely.