A patient with multiple myeloma was initially seen with Bence Jones-type kappa proteinemia and intermittent Bence Jones proteinuria. In the late stage of the disease, involvement of the CNS was observed, and abnormal plasma cells were found in the CSF. Chromosomal analysis of these plasma cells showed an accessory chromosome in the A2 group and an abnormal chromosome in the D13 group. In addition to Bence Jones-type kappa protein similar to that in the serum, the CSF contained IgA-kappa M component. Immunoquantitation detected 250 mg/dL of IgA in the CSF and only 33 mg/dL in the serum. T our knowledge, such discordance of M components has never been described before.