A collaborative randomized clinical trial on the intravesical administration of Adriamycin (ADM) with or without verapamil (VR), a calcium-channel blocker, as chemotherapy of superficial bladder cancer (Ta, T1) was carried out at two universities, Okayama and Kagoshima, and their affiliated hospitals. Arm A consisted of ADM given at 50 mg/50 ml saline, and arm B consisted of ADM given at 50 mg/40 ml saline plus five ampules (25 mg/10 ml saline) of injectable VR. The drugs were instilled into the bladder for 3 consecutive days, and three such courses were given with a 4-day interval between each course for a total of nine instillations. A total of 96 patients (48 in arm A and 48 in arm B) were entered into this study. The two treatment groups showed no significant difference in background factors. Of the 40 evaluated arm-A patients, 24 (60.0%) showed a response (CR + PR), whereas 19 (48.7%) of the 39 patients in arm B responded. The difference between these response rates was not statistically significant. As for adverse reactions to the intravesical chemotherapy, local inflammatory symptoms were observed in half of the patients, although no systemic reaction was observed. No significant difference was found between arm A and arm B, except for urinary turbidity. In conclusion, at the dose employed in the present clinical trial, there was no clear enhancement of the effect of ADM combined with VR in patients with superficial bladder cancer. Further clinical studies are required to determine the optimal doses of ADM and VR for their combination in intravesical chemotherapy.