Ovarian cancer ranks the most lethal among gynecologic neoplasms in women. To assess the immunohistochemical expression of IOR C2 antigen in normal tissues as well as in ovarian cancer, the immunohistochemical expression of IOR C2 in two ovarian cancer cell lines, frozen tissues from both fetus and adult healthy persons, tissue biopsies from normal ovary and ovarian tumors were investigated. IOR C2 immunoreactivity was also compared with the staining pattern of CEA and CA-125. IOR C2 was detected in both epithelial and glandular derivative cells of gastrointestinal tract and cell secretion substance. A limited number of normal tissues tested were positive. Normal human ovarian surface epithelium was no reactive. Intense and heterogeneous immunostaining was detected in 63, 6% of tumor samples studied. Nevertheless, a decreased or lack of IOR C2 over expression in benign cystadenomas was observed contrasting with strongest signal in ovarian carcinomas. IOR C2 was mainly found in mucinous tumors compared to serus and endometroid subtype. No reaction in clear cell carcinoma was observed. IOR C2 shows a differential expression during malignant transformation, as well as in ovarian tumors related to the histological subtype. This glycoprotein may be represents a potential cell surface target for the immunotherapy of cancer using monoclonal antibodies.