To investigate the immune response of patients with gynecologic cancer to a new cancer-related fetal antigen (OFA-1), anti-OFA-1 was titrated by the immune adherence method in these patients. A high prevalence of anti-OFA-1 was observed in a number of different histologic types of tumor and this fact shows that OFA-1 can be highly immunogenic in patients. Then in order to identify anti-OFA-1 profiles that correlate with prognosis and to understand the role of anti-OFA-1 behavior in vivo, I analyzed the anti-OFA-1 response of various gynecologic cancer patients in relation to the course of their disease. 1) Cases which had persistently high anti-OFA-1 levels following surgery and ones in which anti-OFA-1 titer increased to more than twofold were free of clinical diseases. 2) In cases in which anti-OFA-1 antibody increased and then dropped gradually, this was followed by clinical recurrence or metastasis. 3) Cases without response to OFA-1 were associated with no recurrence. Thus monitoring anti-OFA-1 in patients could have immediate clinical application in evaluating prognosis.