By using an immunoglobulin-enzyme bridge method, pregnancy-specific beta 1-glycoprotein (SP1) and placenta-specific tissue proteins (PP5, PP10, PP11, PP12) were investigated in 15 cases of mucinous cystadenocarcinoma and 20 cases of serous cystadenocarcinoma. These proteins could be detected in the cytoplasm of some malignant cells. In mucinous cystadenocarcinomas, SP1, was present in 53.3% of cases, PP5 in 80.0%, PP10 in 20.0%, PP11 in 66.7% and PP12 in 46.7%. In serous cystadenocarcinomas, SP1 was present in 35.0% of cases, PP5 in 76.2%, PP10 in 9.5%, PP11 in 57.1% and PP12 in 23.8%. No proteins were detected in five normal ovaries. All control sections incubated with phosphate-buffered saline or normal, non-pregnant, non-immune rabbit serum in place of the first specific antiserum as well as with the antisera exhaustively absorbed with the corresponding purified antigens were negative for each protein. The detection rates are discussed in relation to the clinical stages and survival rates of the patients. This study suggests that these proteins, especially PP5 and PP11, may be useful as markers in monitoring patients with ovarian adenocarcinomas as well as for their early diagnosis.