The usefulness of 5'-DFUR in both patients with uterine cervical and ovarian cancers was investigated by determining pyrimidine nucleoside phosphorylase (PyNPase) activities and 5-FU levels in cancerous and normal tissues resected from them after oral administration of 5'-DFUR. In uterine cervical cancer, each group of 9 cases administered single dose of 400 mg of 5'-DFUR and 7 cases administered 400 mg of 5'-DFUR 3 times a day continuously for 7 days was investigated. In ovarian cancer, all of 9 cases were administered 400 mg of 5'-DFUR 3 times a day continuously for 7 days. In conclusion, PyNPase activities in the tissues of uterine cervical and ovarian cancers were higher than those in the normal tissues. 5-FU tissue levels in the cancerous tissues were significantly higher than in the normal tissues and blood as well. This tendency was observed in each of the single and continuous administration groups. These results suggest that the tumor selectivity which is one of characteristics of 5'-DFUR could be expected also for cancer in the field of gynecology.