On the basis of previous experiences indicating that the anti-oxidant agent Cu/Zn superoxide dismutase (SOD) is an effective drug in reducing acute and late radiation-induced tissue injury, in the Center of Radiotherapy and Oncology of Catalonia, Barcelona, Spain in 1990 we implemented a randomized prospective study to analyze the incidence and grade of side effects in a group of bladder cancer patients. After surgery patients were randomly allocated to receive either: Option A: Radiotherapy or Option B: Radiotherapy + SOD 8 mgr/IM/day, after each radiotherapeutic application. Between January 1990 and January 1995 a total of 448 patients were included (226 A/ 222 B). Apart from cutaneous side effects, a highly significant incidence of radioinduced acute cystitis and rectitis was detected in patients not treated by SOD. Which was similar to the delayed side effects. From our data we can conclude that SOD is effective in decreasing acute radioinduced damage, and also in preventing the appearance of more delayed disorders.