Thirty one patients with bladder carcinoma of different grades and stages were treated by endoscopic surgery and oral administration of bacillus Calmette-Guerin (BCG). They were randomly separated in two groups: one was treated surgically and the other was treated surgically and with the BCG. According to the ability to develop an immune response to the antigens, patients were divided into three groups. The group who had been treated by endoscopic surgery only had 7 patients with recurrent bladder cancer during a median interval of 30 months. The group treated surgically and with BCG had only one patient with bladder cancer recurrence within a median follow-up period of 30 months. The results obtained with the use of BCG inducing tumor regression seem to indicate a favorable response.