In order to elucidate the effect of tumor vascularity on a various regimens concentration in tumor tissue, correlation among tegafur, 5-fluorouracil (5-FU), uracil concentrations in tissue and the microangiography were examined in 27 patients with colorectal cancer after preoperative administration of UFT (400 mg/day for 7 days). The concentrations of tegafur, 5-FU and uracil in tumor were higher than those in normal tissue (p < 0.01). There was no definite correlation between tissue concentration in each regimen and the extra or intramural vascular changes. A significant high concentration of 5-FU was found in the protuberant cancer and the ulcerative cancer with horizontal growth than that in the ulcerative cancer with vertical growth (p < 0.05). The present study indicates that the vascular changes within a tumor and the vascular pattern of tumor may be a contributing factor affecting the tissue concentration in the regimens.