This study was performed to assess the significance of plasma level and histochemical character of carcinoembryonic antigen(CEA) in early diagnosis and prognosis of ovarian tumor. Plasma level of CEA was measured using EIA method and immunohistochemical tissue staining of CEA was done using biotin-strepto avidin complex immunoperoxidase technique. The percentage of patients with positive CEA level(above 2.5 ng/ml) was 23.1%(6/26) in malignant ovarian tumor and 15.6%(12/77) in benign ovarian tumor. Positive tissue staining of CEA was 42.3%(11/26) in malignant ovarian tumor and 19.5%(15/77) in benign ovarian tumor. In histologic typing, positive tissue staining of CEA was 18.1%(2/11) in serous cystadenocarcinoma, 85.7%(6/7) in mucinous cystadenocarcinoma, 37.5%(3/8) in other malignant ovarian tumors, 7.1%(1/15) in serous cystadenoma, 7.1%(1/14) in mucinous cystadenoma and 27.1%(13/48) in other benign ovarian tumors. Among 5 cases of malignant ovarian tumors with positive CEA level, 3 cases(60%) showed positive tissue staining of CEA, whereas among 21 cases of malignant ovarian tumors with negative CEA level, 8 cases (38.1%) showed positive tissue staining of CEA. However, among 11 cases of benign ovarian tumors with positive CEA level, 4 cases(36.4%) showed positive tissue staining of CEA, whereas among 66 cases of benign ovarian tumors with negative CEA level, 11 cases(16.7%) showed positive tissue staining of CEA. In the 3 year follow-up study of 12 cases with malignant ovarian tumor, among 3 cases with positive tissue staining of CEA, 2 cases(66.7%) survived. In 9 cases with negative tissue staining of CEA, 6 cases(66.7%) survived. In conclusion, these results suggest that the measurement of tumor CEA may be of value in the differential diagnosis of malignant and benign ovarian tumor, especially in diagnosing mucinous cystadenocarcinoma. However, due to the small amount of cases available for study, it was difficult to determine the correlation between the prognosis and tissue CEA staining of ovarian tumors.