Superficial bladder cancer and particularly carcinoma in situ has the potential for invasiveness for which the treatment is cystectomy with a resultant disappointing 50 per cent five-year survival and urinary diversion with a certain diminished quality of life. BCG therapy is a new method of treating aggressive superficial bladder cancer with better response rates than conventional chemotherapy. It may be immunologically mediated and, if so, may be the first major success of a therapeutic modality that offers less morbidity than the currently standard options of surgery, radiotherapy, or chemotherapy.