BACKGROUND: In carcinoma of the bladder, both intravesical chemotherapy and immunotherapy can induce tumor regression and reduce the rate of recurrence, but the relative merits of these two therapies are unclear. We conducted a multi-institutional study to address this question. METHODS: Patients with rapidly recurrent (stage Ta and T1) or in situ transitional-cell carcinoma of the bladder were randomly assigned to receive either doxorubicin administered intravesically or bacille Calmette-Guérin (BCG) administered both intravesically and percutaneously. The 262 eligible patients were followed for a median of 65 months. Complete responses to treatment of carcinoma in situ were confirmed by biopsy and cytologic analysis of the urine. RESULTS: For patients with Ta and T1 tumors without carcinoma in situ, the estimated probability of being disease free at five years was 17 percent after doxorubicin, as compared with 37 percent after immunotherapy with BCG (P = 0.015). The median times to treatment failure (termination of treatment, due to persistence, recurrence, or progression of disease) were 10.4 and 22.5 months, respectively. For patients with carcinoma in situ the complete-response probability estimates (i.e., the estimated probability of documented disappearance of disease) were 34 percent for doxorubicin (23 of 67 patients) and 70 percent for BCG (45 of 64 patients) (P less than 0.001); the median times to treatment failure were 5.1 and 39 months, respectively. The probability of being disease-free at five years survival among the patients with carcinoma in situ was 18 percent after treatment with doxorubicin and 45 percent after BCG therapy. Patients treated with BCG had a higher incidence of toxic systemic effects and a larger number of local irritative symptoms than patients treated with doxorubicin, but few of these adverse reactions were severe. CONCLUSIONS: As compared with intravesical doxorubicin, immunotherapy with BCG provides improved protection against the recurrence of superficial bladder cancer.