We have investigated the effect of verapamil on the cytotoxicity of adriamycin and mitomycin C with human bladder cancer cell lines T-24 and JTC-30. The concentration of verapamil was 10 M, and adriamycin and mitomycin C were used at the concentrations ranging from 10(-2) micrograms/ml to 10 micrograms/ml. The efficacy of drugs were evaluated using cytotoxicity and colony forming assays. Judging from the results of these assays, no significant difference was observed between the drugs in combination with verapamil and drugs alone. The results indicate verapamil has no enhancement for the cytotoxic activity of the anticancer drugs when cell lines T-24 and JTC-30 are used.