With an enzymatic technique, serum sialic acid (SA) levels were determined in patients with gynecologic tumors. Since the SA level for healthy females was 57.4 +/- 7.3 mg/dl, we set the upper normal limit of this parameter at 72 mg/dl. The SA level became larger in ascending order of uterine myoma, benign ovarian tumor, cervical cancer, corpus cancer, and ovarian cancer. The SA level proved to be significantly higher in cancer patients showing poor prognosis than in those having good prognosis irrespective of the category of therapy and it reflected well the clinical course of cancer patients. In patients who receive a combination therapy and need to be followed up for a long term, complete follow-up is sometimes impossible with tumor-derived markers alone. Even in such cases, the sialic acid level will work as a useful follow-up marker because it is nonspecific to histologic types of cancer.