HER-2/neu (c-erb-2) gene encodes a membrane receptor related to the epidermal growth factor receptor and its amplification has been correlated with a shorter disease free interval in breast cancer patients. Recently, clinical trials have shown that treatment with an antibody can block growth of cells expressing HER-2/neu and prolong survival of patients. An immunohistochemical (IHC) test and fluorescence in situ hybridisation (FISH) are used to predict HER-2/neu status. IHC is economic to use and included in routine diagnostic services. However, IHC sensitivity varies between laboratories. In order to ensure reproducibility of results a standard control is needed so that day-to-day variation can be monitored. The objective of this study was to develop a control for HER-2/neu histochemical detection by investigating four breast and ovarian cell lines.