MAGE genes encoding tumor-rejection antigens recognized by cytotoxic T lymphocytes are expressed at the mRNA level in various malignant tumors. We have investigated the expression of genes MAGE-1, -2, -3/-6 and -4a/-4b at the mRNA level in malignant and non-malignant ovarian tumors as well as in normal ovaries by reverse transcription-polymerase chain reaction. MAGE-1, -2, -3/-6 and -4a/-4b were expressed in 12, 5, 11 and 4 of 58 malignant tumors, respectively. The majority of these MAGE-mRNA-positive tumors were histologically surface-epithelial-stromal tumors, in particular serous adenocarcinomas. They mostly consisted of either advanced-stage or recurrent tumors. In contrast, neither benign tumors nor normal ovaries expressed any of the MAGE genes investigated. A 46-kDa MAGE-1 protein was identified in MAGE-1-mRNA-positive serous adenocarcinomas by immunoblot analysis with polyclonal anti-MAGE-1 antibody. These results provide important information for specific immunotherapy of ovarian serous adenocarcinomas with MAGE gene products.