Ectopic production of the immunoreactive beta-subunit of human chorionic gonadotropin (IR-hCG beta) by gynecologic malignancies has been well recognized, but IR-hCG beta has not yet been established as a clinically useful tumor marker, except for germ cell tumors. We measured the concentrations of IR-hCG beta-related molecules, intact hCG, free hCG beta, and beta-CF, in the sera and urine of patients with various gynecologic cancers (cervical, endometrial, and ovarian cancers) to assess their clinical usefulness as a tumor marker in comparison with serum tumor markers such as CEA, SCC, CA125, and CA19-9. The highest incidence of IR-hCG beta was obtained in the assay for beta-CF in the urine, with positive rates of 47.7% (94 of 197) for cervical, 37.8% (14 of 37) for endometrial, and 84.4% (38 of 45) for ovarian cancers with a cut-off value of 0.2 ng/mg of creatinine. In cervical cancer, there was no significant correlation between the concentrations of urinary beta-CF and serum SCC, and 57.9% (114 of 197) of the patients were detected by the combination assay of these tumor markers. Serial determination in 22 cervical cancer patients with elevated urinary beta-CF level prior to therapy showed that its level decreased after successful treatment, but 4 of 5 patients with persistent or recurrent disease had elevated levels of urinary beta-CF. All of the ovarian cancer patients examined were detected by the combination assay of urinary beta-CF and serum CA125. The levels of urinary beta-CF showed little correlation with those of the serum tumor markers, indicating the usefulness of the combination assay of urinary beta-CF with serum tumor markers for detecting cervical and ovarian cancers.