Elevated IgG distributed in oligoclonal bands is characteristically observed in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS) or subacute sclerosing panencephalitis (SSPE)^1–6. Similarly, IgG in bands has been detected in neutral saline (NS) and acid eluates of brain material from these two diseases^7–21. We have now used isoelectric focusing (IEF) to compare IgG eluted from control brain, three plaques and a white matter pool of an MS brain, and three regions of an SSPE brain. A direct peroxidase-conjugated anti-human IgG staining technique was used to stain IgG exclusively and to visualize the minute amounts of IgG obtained from individual MS plaques. Eluates from individual MS plaques have distinct IgG patterns; in contrast, those from separate SSPE brain areas have essentially identical IgG patterns. The identical IgG patterns in three areas of SSPE brain suggest a common response to the same antigen. The different IgG patterns among MS plaques suggest: (1) variable response to the same ‘MS antigen’ in each plaque, (2) response to different MS antigens in different plaques, (3) synthesis of ‘nonsense’ antibodies irrelevant to the pathogenesis of MS in each plaque, or (4) some combination of the above.