Immunohistochemical determinations of carcinoembryonic antigen, α-fetoprotein, human chorionic gonadotropin (hCG), and human placental lactogen (hPL) were performed on tissue sections from 137 epithelial ovarian cancers. Fewer than 25% of serous cystadenocarcinomas contained detectable amounts of any marker. Carcinoembryonic antigen was present in over 50% of tumors, and was noted most frequently in mucinous, endometrioid, and clear cell carcinomas. hPL was demonstrated in 30% of endometrioid carcinomas but was rarely present in other cell types. Both α-fetoprotein and hCG were noted in fewer than 10% of all major cell types of epithelial ovarian cancer. Forty-five patients had serial determinations of plasma levels of carcinoembryonic antigen at the time of regular follow-up visits. Serial plasma levels of carcinoembryonic antigen accurately predicted recurrence in nine of 16 patients whose tumors contained carcinoembryonic antigen, in contrast to two of 16 patients whose tumors were devoid of antigen.