The Japanese Urological Cancer Research Group has conducted three randomized clinical studies on intravesical chemoprophylaxis of superficial bladder cancers. This paper presents a comparative analysis of the first and second of these. The protocol used in the first study was a so-called short-term schedule in which drugs (for group A, ADM 30 mg/30 ml; group B, ADM 20 mg/40 ml; group C, MMC 20 mg/40 ml; and group D, control) were administered twice a week for 4 weeks after transurethral resection (TUR), and in the second study a long-term schedule was used, in which drugs (for group E, ADM 30 mg/30 ml; group F, ADM 20 mg/40 ml; group G, MMC 20 mg/40 ml; and group H, control) were administered twice a week for 1 week, every 2 weeks for 7 weeks, monthly for 8 months, and finally once every 3 months for 1 year. In the first study 575 patients were evaluated and followed up for 5 years. The second study started 28 months later, and 607 patients were evaluated. A generally good prophylactic effect was obtained in the second study when the patients' backgrounds were adjusted in combination with the history and number of the tumors. The second study did not reveal any promoting or inhibitory effect on the progression of the recurrent tumors. There were no significant side effects in either study. The indications and the schedule for prophylactic intravesical chemotherapy should be more carefully studied.