The first clinical results of an ongoing, prospective trial to determine the value of adjuvant Bestatin immunotherapy in the management of bladder cancer are presented. Patients with nonmetastatic transitional cell carcinoma of the bladder, scheduled for full dose local radiation therapy (64 Gy), were randomly allocated to adjuvant oral Bestatin treatment (30 mg daily for at least 1 year), starting at completion of irradiation, or no Bestatin. The longest follow-up period of the 151 evaluable patients is 6 years. The results have shown that the disease-free survival of the patients taking Bestatin is significantly improved compared to the controls (p = 0.04). However, the overall survival of the patients was not affected by the Bestatin treatment. The beneficial effect of Bestatin seemed to be more marked among men than women. Furthermore, statistical analyses of the patient material according to T tumor categories suggested that compared to the controls, patients with less advanced disease (T1 and T2) benefitted more from Bestatin treatment than those with more advanced tumors (T3 and T4). The results of this ongoing trial thus show that patients with bladder cancer benefit from adjuvant Bestatin treatment in terms of disease-free survival.