Orgotein efficacy in minimizing the local side effects induced by radiotherapy, administered to patients suffering from bladder or prostate cancer, was studied in 3 double-blind clinical trials. Assessment parameters such as efficacy, signs and symptoms of bladder disease were chosen as follows: incontinence, pain, dysuria, cystoscopic picture, maximal voiding volume, voiding frequency (day and night), diarrhoea, amount of anti-diarrhoea preparations consumed. In the first study orgotein was administered in a dose of 4 mg, 15-30 minutes after radiotherapy. Orgotein was found to be statistically significant superior to placebo when assessed according to the above mentioned criteria. Side effects that would have compelled stopping the orgotein therapy did not develop. In the second trial 50 patients suffering from prostatic carcinoma received after each radiotherapy (5,400 rad during 6 weeks) 8 mg orgotein or placebo. The radiotherapy-induced side effects were less common in the orgotein group than in the placebo group. The third clinical trial was conducted according to the same protocol as the two previous ones. Fifty patients with either prostate or bladder cancer were given orgotein or placebo in conjunction with radio-therapy. Only data of 26 out of 50 are yet available. These data show in agreement with two previous mentioned trials a significant superiority of orgotein compared to placebo.