Intravesical bacillus Calmette-Guerin for patients with high-risk superficial bladder cancer. Intravesical bacillus Calmette-Guerin (BCG) was employed in the treatment of 55 patients with aggressive superficial transitional cell carcinoma of the bladder (cTa, cT1, cTis). All of the patients had a previous history of recurrent superficial disease, and 41 (75%) were treatment failures following other intravesical therapy. Thirty-six (66%) patients responded to treatment, and 19 (34%) were treatment failures. Twenty-seven (66%) of 41 patients with cTa-cT1 tumors and 9 (64%) of 14 patients with cTis responded, with a mean follow-up period of 30.5 months. Disease progression was noted in 8 (15%) of the patients and muscle invasive disease in 6. Patients with a history of three or more previous events of tumor recurrence, positive urinary cytology, and multicentric disease, all fared worse than patients without these characteristics (p less than 0.05). BCG is an effective agent in controlling superficial transitional cell carcinoma of the bladder, even in a high-risk group of patients who failed previous intravesical therapy. BCG should be employed in this group of patients prior to radical surgery. 