Prophylactic intravesical chemotherapy (IVC) reduces recurrence rates of superficial transitional cell carcinoma (TCC) of the urinary bladder. The patient cohort existed of 86 individuals (stage TaN0M0 or T1N0M0) superficial carcinoma of various grades of malignancy. Following initial transuretheral resection or diagnostic cystoscopy, mitomycin C (MMC), 20 mg dissolved in 50 ml saline, was instilled intravesically by catheter over 1 hr at 2-week intervals, initially and then four more times followed by diagnostic cystoscopy (one course = 12 weeks). Two similar courses were administered thereafter for a total period of 36 weeks. For patients in remission, installations continued in monthly fractionations for 9 more months (cystoscopy every 3 months) and then at 2-month intervals for 12 more months (cystoscopy every 6 months). When cystoscopy revealed recurrence, IVC was repeated from the beginning. No symptoms of MMC-related toxicity were observed. Cystoscopic follow-up evaluations showed a complete response rate of 84% at 3 years and 81% at 5 years after initial therapy. Twenty-seven patients who had not responded to previous treatment with other drugs responded to MMC.