In 296 patients with primary ovarian cancer the sensitivity and specificity of CA125 and carcinoembryonic antigen (CEA) were determined. High CA125 values can be found in serous cystadenocarcinomas, CA125 can also be detected in patients with mucinous carcinomas. Only in cases negative for CA125 should other tumor markers be determined. As a second choice CA72-4 is proposed, since because of its low sensitivity of only 9% CEA should no longer be regularly determined in ovarian cancer. Preoperatively determined CA125 values show no prognostic significance in primary ovarian cancer. The means of CA125 half life in primary therapy demonstrated prognostic significance, and therefore patients with a worse prognostic outcome can be spared the adverse side effects of ineffective chemotherapy.