The influence of N1-(2-tetrahydrofuryl)-5-fluorouracil plus uracil (UFT) on the recurrence of superficial bladder tumors was evaluated in a randomized clinical study. Group A (n = 196) underwent transurethral resection (TUR) and the intravesical chemoprophylaxis, while group B (n = 193) received 400 mg per a day of UFT orally for 6 months in addition to the instillation therapy. These adjuvant therapy was started one week after TUR. Consequently, 30 patients in group B showed UFT-related toxicity and administration of UFT was discontinued in 10 of them. In addition, 87 patients in group B did not complete the 6-month course of UFT administration. Comparison of 2-year actuarial non-recurrence curves revealed no significant difference between groups A and B. However, UFT seemed to have a favorable prophylactic effect when recurrence rates were compared among those patients with recurrent tumors (generalized Wilcoxon: p = 0.1277), and those with recurrent multiple tumors (p = 0.0847).