Analysis of dThdPase levels by high performance liquid chromatography (HPLC) has demonstrated that primary tumor tissues have higher dThdPase activity than adjacent normal tissue of the same organ. Consequently, 5′-dFUrd is preferentially converted to 5-FU in primary tumor tissues after its administration. Among gynecological tumors, however, the relationship between dThdPase activity in the tissues of uterine cervical, uterine endometrial, and ovarian cancers compared with those of adjacent normal tissues has not yet been established. In addition, there have been few reports on the histological localization of dThdPase in gynecological carcinoma tissues. Nevertheless, a report on immunohistochemical staining of uterine cervical carcinoma identified a correlation between survival and immunohistochemical localization of dThdPase. The purpose of the present study is to clarify the relationship between the measured dThdPase activity and its immunohistochemical staining in gynecological cancers.