This study was designed to evaluate the clinical significance of the use of preoperative serum tumor markers in primary epithelial ovarian cancer. Subjects comprised 111 patients with primary epithelial ovarian cancer. Lactate dehydrogenase (LDH), alpha-hydroxybutyrate dehydrogenase (HBDH), carcinoembryonic antigen (CEA), CA19-9, tissue polypeptide antigen (TPA), CA125 and sialyl TN (STN) serum levels were measured within 7 days before surgery. The tumor marker values were compared with the histopathologic diagnosis. The overall agreement between the test results and the actual outcome was calculated using Student's t test and analysis of variance (ANOVA). Survival curves were constructed according to the Kaplan-Meier method, and differences in survival were assessed with the log-rank test. The prognostic significance of tumor markers for survival was assessed in a multivariate analysis with the Cox proportional hazards model. Of the tumor markers examined in this study, CA125 showed the highest positive rate (77.6%), followed by 63.2% for STN and 55.9% for CA19-9. When the positive rate was compared according to histologic types, serous cystadenocarcinoma, mucinous cystadenocarcinoma, endometrioid adenocarcinoma and clear cell carcinoma showed the highest positive rates for CA125 (94.1%), CA19-9 (76.9%), CA125 (91.7%) and STN (75.0%), respectively. Regarding the distribution of tumor marker levels according to the FIGO stage, LDH, HBDH, TPA and CA125 were correlated with the clinical stage while CEA, CA19-9 and STN did not show any correlation. From analyses of tumor marker levels according to histologic types, all patients with a ratio of CA125 to CEA of >1, 000 had serous cystadenocarcinoma and a ratio of CA125 to CA19-9 of >50 showed serous cystadenocarcinoma or endometrioid adenocarcinoma. On the other hand, all patients with a ratio of LDH or HBDH to CA19-9 of <1.0 had mucinous cystadenocarcinoma or clear cell carcinoma. From univariate analysis, the survival time of patients with elevated CA125, TPA or STN was significantly shorter than that of patients with normal CA125, TPA or STN levels. When the Cox's proportional hazard model was used, we identified age, clinical stage, clear cell carcinoma and serum STN as independent prognostic factors. Serum CA125, TPA or STN may give significant prognostic information in epithelial ovarian carcinoma. It is noteworthy that STN has been identified as an independent prognostic factor and has a high rate of positivity in clear cell carcinoma.