Contribution of our experience in 66 patients included in a prospective randomized study to compare the efficacy of Mitomycin C (MMC) and Alpha 2B Interferon (IFN) in the prevention of relapse of vesical surface tumours. Thirty-five patients were included in the MMC arm, 29 of which completed the treatment. Thirty-one patients were included in the IFN arm, 26 of which are evaluable. MMC was given endovesically at a rate of 30 mg weekly for one month, and then monthly to complete one year. Through the same route, 50 million units of IFN were given weekly for 3 months, and then monthly to complete one year. Within the MMC arm, three patients (10.3%) showed progress, twelve patients (451.3%) relapsed, and seventeen (58.7%) are disease free. With regard to IFN treated patients, one patient (3.8%) showed progress, ten (38.4%) relapsed, and sixteen (61.6%) are disease free. We conclude that there are no significant differences between these two drugs.