The extent to which the antigenic phenotype of human epithelial ovarian cancer changes during the course of the disease is an issue that must be addressed in order to maximize the potential of antibody-directed imaging and therapy. We have obtained tumor specimens at two separate operations from ten patients with epithelial ovarian cancer and typed these specimens with a panel of 19 monoclonal antibodies to cell surface glycoprotein and carbohydrate antigens including blood group antigens. Antibodies with relatively high specificity for malignant cells as well as those detecting more widely distributed epithelial antigens were used in the study. Mean time between the two operations was 8.5 months. Five patients received intraperitoneal therapy during the interval between the two operations, including platinum-based regimens (four patients) and tumor necrosis factor (one patient). Four patients received intravenous platinum-based chemotherapy; one received no treatment. Frozen sections of specimens were stained with the antibodies by the indirect immunoperoxidase technique. Antigenic phenotypes were found to be unrelated to the patient's age, stage, tumor grade, histologic cell type, prior chemotherapy, and interval between operations. Most significantly, little difference was seen in antigenic expression between tumors obtained at the two operations for either the cell surface or blood group markers. Variations in the staining pattern were seen with antibody B72.3 and, to some extent, with the anti-blood group antibodies, which are known for producing heterogeneous staining. The antigenic phenotype of the tumor specimens in a given patient as determined immunohistochemically by our panel of antibodies showed only minor variation between operations, even under the selective pressures of chemotherapy and immunotherapy.