We present a case of a 63-year-old man who was diagnosed CML at the onset of bladder transitional carcinoma. He had been treated with subcutaneous injection of natural interferon-α at the dose of 2×10⁶ U on consecutive days. Four weeks later, he achieved remission and then received curative operation. Ph¹ chromosome transiently decreased to 40%. For more than 16 months, he remained in remission. Since in CML Ph¹ clone can be found in B cells and CML itself may result in hypogammaglobulinemia which may be basis of carcinogenesis, it was speculated that hypogammaglobulinemia found in this case related to carcinogenesis.