Both intravesical mitomycin C (MMC) and bacillus Calmette-Guérin (BCG; Pasteur strain F) were effective in the present prospective randomized multicenter study consisting of 91 patients with frequently recurrent superficial (Ta-T1) bladder cancer. The result was in favour of BCG, as shown by the measurements with complete response (CR), disease-free interval and recurrence rate. CR of 58% with MMC and 40% with BCG were reached in 22 instillation series on carcinoma in situ of 18 patients. Due to side effects, MMC instillations were discontinued in 8.6%, and BCG instillations in 19.6%, respectively. After the 2-year follow-up also 1 case of pulmonary tuberculosis occurred in the BCG group.