Epidermal growth factor receptor (EGF-R) was studied with monoclonal antibody 2E9 on 50 ovarian tumors of various histological types and 10 non-tumorous ovarian tissues by immunohistochemistry. Enhanced expression was observed in 26/50 (52%) of the tumors. Only 25 out of 46 epithelial tumors (54%) showed positivity in epithelial tumor cells. Staining was cytoplasmic in all cases. No correlation was established between EGF-R expression and the histological type of the epithelial tumor. Apart from EGF-R expression in tumor cells, low immunoreactivity was also observed in stromal and endothelial cells in both normal and tumorous ovarian tissues. Furthermore in 8/9 specimens containing necrotic areas, EGF-R was noticed in these areas as well. Both of the latter observations may have impact on the evaluation of the prognostic value of EGF-R activity in tumors, when based on EGF-R measurements using biochemical binding studies. We therefore recommend that EGF-R is measured with both methods in studies regarding its clinical value.