In recent years several novel prognostic determinants of breast cancer have been identified, including HER-2/neu. The oncogene called HER-2/neu or c-erbB-2 located at 17q21 encodes a 185-kD transmembrane glycoprotein, p185. The HER-2/neu gene is frequently overexpressed in human breast cancers as a result of gene amplification and/or elevated transcription. In this study we investigated the association between the presence of HER-2/neu gene ampliflcation and appearance and/or progression of breast cancer. Paraffin embedded tumour tissue was obtained from 82 women with breast cancer. Blood samples from age matched healthy women served as control (n = 50). The amplification of HER-2/neu gene was determined by PCR amplification using appropriate primers. The amplification of HER-2/neu gene was significantly higher in women with breast cancer as compared with control (P < 0.05). Additionally, there were differences in the amplification status between node-positive and node-negative breast cancer patients. The results suggest that the presence of amplification of HER-2/neu gene may be linked with the appearance and/or progression of breast cancer.