In an attempt to prevent, delay, or reduce further tumor occurrence, 88 patients with recurrent, superficial carcinoma of the urinary bladder were randomly assigned to receive either standard therapy (cystoscopy with fulguration) or standard therapy and bacillus Calmette-Guérin (BCG). BCG was administered intravesically and percutaneously once weekly for 6 weeks. No serious toxicity was seen. There were 43 evaluable patients in each of the two groups. Results in the BCG group versus the control group were as follows: reduction in the number of recurrent tumors (43 vs 27 patients [P less than 0.001] ); conversion to negative cytology (11 of 33 vs three of 34 patients [P less than 0.05] ); and tumor progression requiring cystectomy (three vs 15 patients [P less than 0.001] ). Disease-free interval (P less than 0.001), time with negative cytology (P less than 0.001), and time to progression of disease (P less than 0.003) were longer in patients treated with BCG. These results indicate that the combination of standard therapy and BCG is more effective than standard therapy alone in patients with recurrent superficial bladder tumors.