FD-1, 1,3-bis(tetrahydro-2-furanyl)-5-fluorouracil, is an anticancer agent newly developed in Japan and is a kind of marked compound of 5-fluorouracil. FD-1 changes to 3-FT and tegafur and is then converted to 5-fluorouracil. From our clinical observations, FD-1 showed excellent clinical effects in a daily dose of 600 mg. However, in some instances toxicities of central nervous system were developed. On the other hand, there is evidence that uracil enhances antitumor activity of FD-1 in the treatment of sarcoma 180 bearing mice and AH130 bearing rats. On oral administration of FD-1 plus uracil in various combination ratios, the high T/B value (ratio of the concentration of 5-fluorouracil in the tumor and blood) is obtained at a ratio of uracil to tegafur of 20 to 50. Fifteen cases with advanced cancer were treated with UFD-1 (mixture of FD-1 and uracil under molar ratio of 1: 20) in a daily dose of 300 mg of FD-1. However, no tumor regression was observed in any of our cases. On the contrary, toxic manifestations were experienced in five of fifteen cases. They mainly consisted of mild G.I. toxicities. Furthermore, in one case, ataxia developed. Our clinical studies revealed no usefulness of UFD-1 in the treatment of advanced adenocarcinoma cases.