In order to verify the antitumor activity of fluorinated pyrimidine drugs, we conducted an investigation of the clinical pharmacology with two drugs, 5'-DFUR and UFT. Total 21 cases of cervical cancer were alloted randomly into 5'-DFUR group (daily dose 800 mg for 3 days) consisting of 11 patients and UFT group (daily dose 600 mg for 3 days) consisting of 10 patients, the unchanged substances (5'-DFUR in the 5'-DFUR group and tegafur concentrations in the UFT group) and 5-FU concentrations in serum and tissues were measured 6 hours after administration of the drugs. The 5'-DFUR concentration in the 5'-DFUR group was not detected in serum and less than a detectable limit for all of cancerous tissues, normal cervical tissues, and lymph nodes. The tegafur concentrations in the UFT treated group was 13.8 +/- 7.0 micrograms/ml for serum, 10.4 +/- 6.4 micrograms/g for cancerous tissues, 14.1 +/- 7.3 micrograms/g for normal cervical tissues, and 4.5 +/- 4.2 micrograms/g for lymph nodes. The 5-FU concentrations in the 5'-DFUR treated group were 0.018 +/- 0.046 micrograms/g for cancerous tissues, but less than a detectable limit for serum and normal cervical tissues. On the other hand, in the UFT group, 0.271 +/- 0.247 micrograms/g for a cancerous tissue, 0.035 +/- 0.018 micrograms/ml for serum, 0.125 +/- 0.073 micrograms/g for normal cervical tissues, showing significantly high values (p < 0.01, p < 0.001, and p < 0.01, respectively) compared to those in the 5'-DFUR treated group. These results suggest that UFT is a promising drug for the treatment of cancer of the uterine cervix.