To evaluate the effect of UFT on nuclear DNA distribution of carcinoma, we measured the DNA content of biopsy specimens and resected specimens obtained from 18 patients by microfluorometry. The tumors consisted of 7 gastric and 11 colorectal carcinomas. Five patients who received administration of 400mg of UFT (400mg of tegafur) were classified as the chemotherapy group and another 13 patients were classified as the control group. 1) DNA indices of biopsy specimens and resected specimens of the same patients showed almost the same values both in the control group (r = 0.81) and in the chemotherapy group (r = 0.89) (p less than 0.05). 2) S and S + G2M fractions of resected specimens showed almost the same values as compared with those of corresponding biopsy specimen in the control group. However, in the chemotherapy group S and S + G2M fractions of resected specimens showed a tendency to be higher than those of corresponding biopsy specimen (0.05 less than p less than 0.1). This study indicates that the biopsy specimens are sufficient for DNA analysis and that UFT-induced DNA change may be increase of S and S + G2M fraction.