Tumor markers CA 125, CA 19-9, and carcinoembryonic antigen (CEA) were detected by immunohistochemistry in paraffin embedded tissue samples obtained from two different locations in 35 ovarian tumors. In addition, serum concentrations of these tumor markers were measured before cytoreductive surgery. The staining reaction was heterogeneous in different parts of the tumor as well as within the parenchyma. Of the marker positive tumors, a staining reaction was observed in both tissue samples in only 10 of 22 cases for CA 125, in eight of 13 cases for CEA, and in three of eight cases for CA 19-9. Eighty-one percent of the patients whose tumor was positive for CA 125 also showed elevated serum levels of this marker. A poor correlation was found between tissue and circulating CA 19-9 levels. CEA was detected in 28% of the tumors and seemed to be valuable only for monitoring in rare cases of ovarian cancer. For purposes of selecting a marker for monitoring of patients with ovarian carcinoma, immunohistochemistry has a predictive value for CA 125 only. In order to better define the marker expressed in a tumor, it is necessary to examine at least two samples of different parts of the malignant tissue.