Analysis of antigen expression at multiple tumor sites in epithelial ovarian cancer. The question of whether the antigenic phenotype of human epithelial ovarian cancer varies in a given patient between the primary tumor and metastatic sites or among metastatic sites themselves is an important issue in planning potential therapeutic strategies for ovarian cancer. We have obtained tumor specimens from at least two separate sites during operations on 12 patients with epithelial ovarian cancer, and we have typed these specimens with a group of 18 monoclonal antibodies that react with cell-surface glycoprotein and carbohydrate antigens, including blood group antigens. Antibodies with relative specificity for malignant cells as well as those that detect more widely distributed epithelial antigens were used. A total of 31 specimens from 12 patients with advanced adenocarcinoma (8 serous, 3 undifferentiated, 1 endometrioid) of the ovary were studied, including fresh ascites cells in two patients. Frozen sections of tumor specimens were stained with the antibodies by the indirect immunoperoxidase technique and graded semiquantitatively. Little difference was seen in antigenic expression of tumors that were obtained from various sites in the same patient for either the epithelial cell markers or blood group markers. Intratumoral antigenic heterogeneity was seen, but this was generally quite consistent within a given patient's specimens. As anticipated, variations in antigen expression were seen among specimens from different patients. The antigenic phenotype of the tumor specimens in a given patient, as determined immunohistochemically by our group of antibodies, showed only minor variation among primary and metastatic sites. 