The overexpression of two members of the erbB oncogene family-the epidermal growth factor receptor protein (EGF-R) and the HER-2/neu protein-in breast cancer has been investigated by numerous authors. Their exact role in breast cancer is still not defined. The simultaneous investigation of EGF-R and HER-2/neu in the same study population has only rarely been performed in breast cancer. Therefore, we analyzed the EGF-R and the HER-2/neu protein expression in 142 breast cancer specimens and 12 benign breast samples by immunohistochemistry. Results of the different expression analyses were compared with established clinicopathological parameters including estrogen and progesterone receptor status. In our study group EGF-R expression correlated with advanced tumor stage, axillary lymph node status and histological grade. HER-2/neu expression correlated with larger tumor size. Neither the evaluation of a single parameter of the erbB family nor the combination of both parameters showed a significant correlation with the disease-free and the overall survival of the individual patient with breast cancer. Only the expression of the progesterone receptor correlated with a better overall survival. Steroid hormone receptor expression and the expression of EGF-R and HER-2/ neu seem to be two independent phenomena in our samples of breast cancer. The simultaneous evaluation of EGF-R and HER-2/neu expression did not lead to new information of prognostic relevance.