Although bacillus Calmette-Guerin (BCG) has been recognized as an effective therapy for superficial bladder cancer, dose-response studies are not available. Such studies are important because the administration of the vaccine is not devoid of significant side effects when the standard dose of 120 mg. is used. It has been speculated that smaller doses may be equally effective but carry fewer side effects. A controlled study comparing 2 doses of BCG was conducted as an initial step to explore this possibility. A total of 97 patients with a diagnosis of superficial (stages TIS, Ta and T1) bladder cancer was assigned to receive either 60 or 120 mg. BCG intravesically weekly for 6 weeks. The higher dose resulted in a better response for stages TIS, Ta (for prophylaxis of recurrence) and T1. However, the differences were not statistically significant. When stage TIS and Ta tumors coexisted, a significantly better response was recorded for the high dose. The overall success for the 2 treatments was 67% and 37% for the high and low doses, respectively. These differences reached statistical significance (p less than 0.02). Side effects were significantly less in number and severity in patients receiving the smaller dose of the vaccine.